A federal grand jury in the US state of Virginia has formally charged former FBI Director James Comey with two offences related to testimony he gave to Congress.

Mr Comey, who has long drawn US President Donald Trump's criticism, is accused of lying to a Senate committee in 2020 about whether he authorised a leak of classified information to the media.

Responding to the indictment, Mr Comey declared himself innocent and said he had "great confidence in the federal judicial system".

The indictment comes days after Trump called on the country's top law enforcement official to more aggressively investigate his political adversaries, including Mr Comey.

An indictment in the US justice system is a formal accusation issued by a grand jury after they review evidence to determine if a case should proceed.

Mr Comey may have his first court appearance on Friday but his arraignment - where charges are formally read out in front of a defendant in court - has been set for 9 October in Alexandria, Virginia, the BBC's US partner CBS reports.

The probe is being led by Lindsey Halligan, the US Attorney for the Eastern District of Virginia, who was previously Trump's personal lawyer and took over her new role on Monday.

Attorney General Pam Bondi, urged by Trump at the weekend to pursue Comey, said in a statement that the indictment "reflects this Department of Justice's commitment to holding those who abuse positions of power accountable for misleading the American people".

The two-page indictment is short on detail but it says Mr Comey has been charged with one count of making false statements and another of obstruction of justice.

Both counts relate to Mr Comey's appearance at a Senate Judiciary Committee in September 2020, when he was questioned about the FBI's handling of two explosive investigations - one on pro-Trump election interference by Russia and another on Hillary Clinton's use of a private email server.

The five-year statute of limitations for charges based on that hearing would have expired next week.

The first count relates to Mr Comey telling the committee he had not authorised someone else at the FBI to be an anonymous source in news reports about an FBI investigation into what the indictment describes as "PERSON 1", believed to be Hillary Clinton.

The second count alleges that Mr Comey "did corruptly endeavor to influence, obstruct and impede" the committee by making false statements to it.

The jury rejected a third count of making false statements.

If found guilty, Mr Comey could face up to five years in prison.

He said in a video statement: "My family and I have known for years that there are costs to standing up to Donald Trump."

"We will not live on our knees, and you shouldn't either," he continued, adding: "And, I am innocent. So, let's have a trial."

The case had recently been handed over to a new prosecutor after Erik Seibert, the original US attorney overseeing the case, was fired by the Trump administration. He was replaced by Ms Halligan.

The case is considered to be the highest-profile indictment of a public figure during Trump's second term.

Trump recently voiced his frustration that prosecutions of his public critics such as Mr Comey, Senator Adam Schiff and New York Attorney General Leticia James are taking so long.

"We can't delay any longer, it's killing our reputation and credibility. They impeached me twice, and indicted me (5 times!), OVER NOTHING. JUSTICE MUST BE SERVED, NOW!!!" Trump said on Truth Social last week.

Asked about Mr Comey hours before the indictment was unsealed, Trump called him a "bad person" but said he had no advanced knowledge of his prosecution.

Laurie Levenson, a former federal prosecutor and a law professor at Loyola Marymount University, said it will be a very challenging case to prosecute.

"It's often the defendant's word against someone else's and you're gonna have to look at the credibility of both," she told BBC News.

"And even if James Comey got things wrong, that doesn't mean that he knowingly or intentionally lied to Congress. So proving that is going to be the heart of the case."

Ms Levenson also said this prosecution and Trump's public pressure to move forward on it suggests that the traditional firewall between the White House and the US Department of Justice had "collapsed with this case".

Several Democrats condemned the charges, with House Democratic Leader Hakeem Jeffries denouncing them as "a disgraceful attack on the rule of law", vowing "accountability" for "anyone complicit in this malignant corruption".

Mr Comey served as the FBI's director between 2013 and 2017.

He had a tumultuous tenure that included overseeing a high-profile inquiry into Democratic candidate Hillary Clinton's emails just weeks before the 2016 election, which she lost to Trump.

He was fired by Trump amid an investigation into Russian interference in the 2016 election.

This is not the first investigation into the former FBI boss to be launched this year.

He was investigated by the Secret Service after he shared and then deleted a social media post of seashells spelled the numbers "8647", which Republicans alleged was an incitement to violence against US President Donald Trump.

The number 86 is a slang term whose definitions include "to reject" or "to get rid of", according to the Merriam-Webster dictionary.

In July, Mr Comey's daughter Maurene Comey was fired from her role as a federal prosecutor in the Southern District of New York. She was given no reason for being removed from the office where she had worked for 10 years, according to media reports.

Earlier this month, she sued the Trump administration over her dismissal.

The Justice Department has been firing lawyers who worked on cases that angered the president, including a special prosecutor investigation of Trump. (BBC)

Update news