In a statement, the president said his son had been “singled out” and called his cases “a miscarriage of justice”.

Hunter Biden pleaded guilty to tax charges earlier in September, and was found guilty of being an illegal drug user in possession of a gun in June – becoming the first child of a sitting president to be a convicted of a crime.

Reacting to the pardon, President-elect Donald Trump said: “Does the Pardon given by Joe to Hunter include the [6 January] Hostages, who have now been imprisoned for years? Such an abuse and miscarriage of Justice!”

Trump was referring to his supporters who stormed the US Capitol on 6 January 2021 in a bid to overturn Trump’s defeat in the 2020 election.

Joe Biden’s full and unconditional pardon for his son comes after the president had previously said he would not give him clemency.

Just a couple of months ago, in September, the White House press secretary said that Biden would not issue a pardon for his son.

But on Sunday evening, President Biden said although he believed in the justice system, “politics has infected this process and it led to a miscarriage of justice”.

“From the day I took office, I said I would not interfere with the Justice Department’s decision-making, and I kept my word even as I have watched my son being selectively, and unfairly, prosecuted,” he said.

Biden said he wrestled with the decision, and added: “once I made this decision this weekend, there was no sense in delaying it further.”

“I hope Americans will understand why a father and a President would come to this decision,” he said.

In a reaction statement, Hunter Biden said mistakes he made during the darkest days of his addiction had been “exploited to publicly humiliate and shame” his family for political sport.

“I will never take the clemency I have been given today for granted and will devote the life I have rebuilt to helping those who are still sick and suffering,” the 54-year-old added.

The younger Biden has been sober for five-and-a-half years, his father said.

This is not the first time a US president has pardoned a member of their family.Bill Clinton pardoned his younger half-brother, Roger Clinton, for a 1985 cocaine-related offence in 2001.

In 2020, Donald Trump pardoned Charles Kushner, the father-in-law of his daughter Ivanka. President-elect Trump has recently announced that Kushner will be the new ambassador to France.

Hunter Biden pleaded guilty to nine counts of federal tax fraud in September, for which he had been facing up to 17 years in prison.

He was also convicted of three felonies in connection with a gun purchase in June, for which he had been facing up to 25 years in prison.

Sentencing for these cases had been scheduled for 12 and 16 December.

His legal troubles had been a dark cloud over his father’s presidential campaign, which came to an end in July after Biden pulled out of the election race.

Biden endorsed Vice-President Kamala Harris to succeed him as the Democratic candidate, who lost the election to Republican Donald Trump in November.

Trump is set to take over the Oval Office from Biden on 20 January 2025 – Inauguration Day.

In a statement, the president said his son had been “singled out”, and called his cases “a miscarriage of justice.”

“From the day I took office, I said I would not interfere with the Justice Department’s decision-making, and I kept my word even as I have watched my son being selectively, and unfairly, prosecuted,” he added.

Hunter Biden pleaded guilty to tax charges earlier in September, and was found guilty of being an illegal drug user in possession of a gun in June – becoming the first child of a sitting president to be a convicted of a crime.

There has been an effort to break Hunter – who has been five and a half years sober, even in the face of unrelenting attacks and selective prosecution,” Biden said in a statement released by the White House.

“In trying to break Hunter, they’ve tried to break me – and there’s no reason to believe it will stop here. Enough is enough.”

Biden’s decision comes weeks before Hunter Biden was set to face sentencing for a string of felonies related to making a false statement about his drug use during a gun background check and failing to pay at least $1.4m in taxes.

The younger Biden had faced a maximum of 25 years in prison in the tax case and 17 years in the firearms case, though he would have almost certainly received much less severe punishment under sentencing guidelines.

In justifying his decision, Biden said that people are “almost never” brought to trial for wrongly filling out a gun purchase form and that those who pay their taxes late usually receive “non-criminal resolutions”.

“For my entire career I have followed a simple principle: just tell the American people the truth. They’ll be fair-minded. Here’s the truth: I believe in the justice system, but as I have wrestled with this, I also believe raw politics has infected this process and it led to a miscarriage of justice – and once I made this decision this weekend, there was no sense in delaying it further,” Biden said.

“I hope Americans will understand why a father and a President would come to this decision.

”In June, Biden had flatly ruled out the possibility of granting his son a pardon or commuting his sentence.

“I said I will abide by the jury decision. I will do that and I will not pardon him,” Biden had said.

The White House had reiterated Biden’s intention not to pardon his son as recently as November 8, when press secretary Karine Jean-Pierre told reporters: “Our answer stands, which is no.”

The FBI said it was aware of “numerous bomb threats” as well as “swatting incidents”, in which hoax calls are made to attract a police response to the target’s home.

Threats were made against at least nine people chosen by Trump to lead the Departments of Defence, Housing, Agriculture and Labor, as well as his pick for US ambassador to the United Nations, among others.

Police are investigating the incidents, which happened on Tuesday night and Wednesday.

Karoline Leavitt, a spokeswoman for Trump’s transition team, said the Trump appointees “were targeted in violent, unAmerican threats to their lives and those who live with them”.

She said “law enforcement acted quickly to ensure” the nominees’ safety.

“With President Trump as our example, dangerous acts of intimidation and violence will not deter us,” she said.

Neither Leavitt nor the FBI identified any of the targets by name.

New York Republican Elise Stefanik, who Trump has named to be the US ambassador to the United Nations, was the first to say her family home had been targeted by a bomb threat.

Her office said the congresswoman was informed of the threat while she was driving with her husband and three-year-old son from Washington DC to New York for Thanksgiving.

Defence secretary nominee Pete Hegseth later confirmed that he was also targeted.

On X, he said that a police officer had shown up at his home on Wednesday morning, as his seven children were sleeping inside to notify him they had received “a credible pipe bomb threat”.

“I will not be bullied or intimidated. Never,” he wrote. “President Trump has called on me to serve – and that is what I intend to do.”

Trump, who survived two assassination attempts during his campaign, was not among those who received the hoax calls, law enforcement sources told US media.

He has received genuine threats recently, according to officials in Arizona who arrested a man earlier this week for posting videos on a “near-daily basis” in which he threatened to kill Trump and his family.

None of those targeted this week were protected by the US Secret Service, according to media reports.

Lee Zeldin, who Trump has nominated to become administrator of the Environmental Protection Agency, also confirmed he was targeted, saying a “pipe bomb threat” was sent to his home with a “pro-Palestinian themed message”.

“My family and I were not home at the time and are safe,” he said. “We are thankful for the swift actions taken by local officers.”

Brooke Rollins, Trump’s pick to lead the Department of Agriculture, posted on X to thank police in Fort Worth, Texas, for their “swift efforts” to investigate a threat to her family on Wednesday morning.

“We were unharmed and quickly returned home,” she wrote.

Scott Turner, Trump’s pick for Department of Housing, and Lori Chavez-Deremer, his pick for Labour Secretary, also posted on social media that they had been targeted. They each vowed that they would not be deterred by the threats.

President Joe Biden has been briefed on the incidents, the White House said in a statement.

“The White House is in touch with federal law enforcement and the President-elect’s team, and continues to monitor the situation closely.

“US Capitol Police, which protects Congress, said in the statement that it was working with federal law enforcement agencies on any “swatting”, but declined to provide further details “to minimise the risk of copy-cats”.

Florida Republican Matt Gaetz, who recently dropped out of the running to become US attorney general, was also targeted.

The sheriff’s office in Florida’s Okaloosa County confirmed that a bomb threat targeted an address in the town of Niceville.

The home’s mailbox was cleared and no devices were located, police said, and a search of the area did not uncover anything.

New York police told CBS News that the New York home of Trump’s nominee for commerce secretary, Howard Lutnick, was also threatened.

Pam Bondi, who was selected to replace Gaetz as Trump’s nominee, was also targeted along with incoming White House Chief of Staff Susie Wiles, according to CBS.

Fox News reports that John Ratcliffe, Trump’s nominee to be director of the CIA, also received threats.

Similar hoax tactics have been recently used against other high-profile political figures, including against the judges and prosecutors who oversaw the criminal cases against Trump.

Last year, US politicians around the country were swatted over Christmas. Most were Republican, but some Democrats were targeted as well.