U.S. Attorney-General Jeff Sessions refused Tuesday to answer questions about the firing of FBI director James Comey, leading Democratic senators to accuse him of "obstructing" and "stonewalling" a legislative committee.

The combative hearing before the Senate intelligence committee – during which Mr. Sessions repeatedly ducked queries about his conversations with U.S. President Donald Trump regarding Mr. Comey – further stoked accusations the administration is trying to hinder investigations into Russian interference in last year's election campaign.

The Attorney-General, for his part, emphatically denied he had conspired with the Kremlin in its campaign to tip the election toward Mr. Trump by leaking embarrassing Democratic party e-mails.

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Read more: What you missed from Jeff Sessions' testimony on Trump, Russia and the 2016 election

"I have never met with or had any conversation with any Russians or any foreign officials concerning any type of interference with any campaign or election in the United States. Further, I have no knowledge of any such conversations by anyone connected to the Trump campaign," Mr. Sessions told the panel, his voice rising with pique.

Any suggestion to the contrary, he said, was "an appalling and detestable lie" and "secret innuendo."

Mr. Sessions insisted his conversations with Russian Ambassador Sergey Kislyak last year were innocuous. One possible encounter – at a reception before a Trump speech at Washington's Mayflower Hotel in April, 2016 – was so inconsequential, he said, he could not remember speaking with Mr. Kislyak there.

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In March, Mr. Sessions recused himself from overseeing a Federal Bureau of Investigation probe into ties between the Kremlin and Mr. Trump's presidential election campaign, after The Washington Post revealed two of Mr. Sessions's meetings with Mr. Kislyak – one at the Republican National Convention last summer, and another two months later at his Washington office. Mr. Sessions had denied at his January confirmation hearing that he ever met with Mr. Kislyak.

Two months after his recusal, Mr. Sessions signed off on Mr. Comey's firing. Mr. Trump acknowledged the sacking was motivated in part by the FBI's Russia probe. Last week, Mr. Comey told the same Senate panel he was fired because the investigation was "irritating" Mr. Trump.

When senators on Tuesday asked Mr. Sessions if he had discussed the Russia investigation or Mr. Comey's firing with Mr. Trump, Mr. Sessions refused to say.

"I'm not able to discuss with you, or confirm or deny, the nature of a private conversation that I may have had with the President on this subject or others," Mr. Sessions said.

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In a series of of testy exchanges, Democratic senators blasted Mr. Sessions's refusal to answer.

"We are talking about an attack on our democratic institutions and stonewalling of any kind is unacceptable … there is no legal basis for this stonewalling," Oregon Senator Ron Wyden said. New Mexico Senator Martin Heinrich accused Mr. Sessions of "obstructing" the committee and "impeding this investigation."

"I am not stonewalling," Mr. Sessions fired back at one point. "You don't walk into any hearing or committee meeting and reveal confidential communications with the President of the United States."

The Attorney-General also refused to discuss reports that Mr. Trump was angry at him for recusing himself from the Russia investigation, as this led to the probe ultimately getting taken over by an independent prosecutor.

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Mr. Sessions said he would not describe his conversations with Mr. Trump in case Mr. Trump ever decides to invoke executive privilege, which is the President's right not to testify in court or before committee. Mr. Sessions acknowledged Mr. Trump has not invoked privilege.

Jeffrey Cramer, a former federal prosecutor, said Mr. Sessions's use of this particular power in Mr. Trump's name was questionable. "The Attorney-General invoked executive privilege on behalf of someone else. It's not only highly unusual, but I'm not sure it's appropriate," Mr. Cramer, a security and business consultant with Berkeley Research Group, said in an interview.

But Mr. Sessions did succeed in tamping down suspicions over his meetings with Mr. Kislyak, Mr. Cramer said, and in particular their possible encounter at the Mayflower. "It certainly doesn't seem like a sinister interaction, as far as we can tell."

Mr. Comey last week said the FBI was "aware of facts" that would have made it "problematic" for Mr. Sessions to be involved in the Russia investigation. CNN reported that Mr. Comey had told senators in a closed-door briefing that agents were investigating another possible meeting between Mr. Sessions and Mr. Kislyak. That encounter appears to have been the one at the Mayflower.

Mr. Sessions acknowledged both he and Mr. Kislyak were at the Mayflower that day, but said he could not remember if they spoke. He also said he was unaware of any other undisclosed conversations between members of Mr. Trump's circle and Russian officials.

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He said he had denied in January ever meeting with Russian officials because he had understood the "rambling" question about it at his confirmation hearing to be asking whether the Trump campaign had colluded with the Kremlin. Mr. Sessions' answer, however, was more categorical than that. He told the Senate then that he "did not have communications with the Russians."