Washington: White House officials said on Friday they did not know yet whether US President Donald Trump would seek to block former FBI Director James Comey from testifying to Congress next week, a move that could spark a political backlash.

"I have not spoken to counsel yet. I don't know how they're going to respond," White House spokesman Sean Spicer told reporters.

Comey was leading a Federal Bureau of Investigation probe into alleged Russian meddling in last year's US presidential election and possible collusion by Trump's campaign when the president fired him last month. Critics have charged that Trump was seeking to hinder the FBI's investigation by dismissing Comey.

The former FBI chief is due to testify on Thursday before the Senate Intelligence Committee as part of its own Russia-related investigation, and his remarks could cause problems for the Republican President.

Comey is widely expected to be asked about conversations in which Trump reportedly pressured him to drop an investigation into his former national security adviser, Michael Flynn, whose ties to Russia are under scrutiny. Critics have said that such pressure could potentially amount to obstruction of justice.

Presidents can assert executive privilege to prevent government employees from sharing information. However, legal experts say it is not clear whether certain conversations between Trump and Comey that the President has talked about publicly would be covered, and any effort to block Comey, who is now a private citizen, from testifying could be challenged in court.

In an interview with ABC News, White House senior adviser Kellyanne Conway appeared to indicate Trump would allow Comey to testify. "We'll be watching with the rest of the world when Director Comey testifies," she said.

But asked directly whether Trump would invoke executive privilege on Comey's testimony, she added: "The President will make that decision."

Amid a political firestorm touched off by Comey's firing, the Justice Department appointed a special counsel, Robert Mueller, last month to take the lead on the Russia investigation. IT was revealed on Saturday Muller is expanding his probe to also include a grand jury investigation into Flynn.

The move means Mueller's politically charged inquiry will now look into Flynn's paid work as a lobbyist for a Turkish businessman, Ekim Alptekin, in 2016, in addition to contacts between Russian officials and Flynn and other Trump associates during and after the November 8 presidential election.

US intelligence agencies have concluded the Russian government sought to influence the US election in Trump's favour, a charge Russia has denied. Russian President Vladimir Putin, however, said on Thursday some "patriotic" Russians may have acted on their own.

Trump, who has raised doubts about the US. agencies' findings and denounced the continuing Russia probes, has denied any collusion.

Reuters