WASHINGTON — James Comey, fired last month as FBI director amid a federal investigation into connections between Russia and the Trump campaign, is set to testify next Thursday at a highly anticipated congressional hearing that could shed light on his private conversations with the president in the weeks before his dismissal.

The Senate intelligence committee announced Comey’s appearance, and a Comey associate said he had been cleared to testify by Robert Mueller, another former FBI director now overseeing that investigation as special counsel.

Also on Thursday, Democrats raised more questions about contacts during the campaign between the Russian ambassador to Washington, Sergey Kislyak, and President Trump’s attorney general, former Sen. Jeff Sessions, R-Ala.

Sessions, a close Trump adviser, withdrew from the Russia investigation in March after acknowledging two previously undisclosed contacts with Kislyak last summer and fall.

Sens. Patrick Leahy, D-Vt., and Al Franken, D-Minn., released a letter urging the FBI to investigate whether Sessions had falsely testified under oath when he said at his January confirmation hearing that he hadn’t had any contacts with Russia.

“If it is determined that the attorney general still has not been truthful with Congress and the American people about his contacts with Russian officials during the campaign, he needs to resign,” the senators wrote.

In addition to the two meetings that Sessions has acknowledged, the senators pointed to the possibility of a separate encounter at an April 2016 Trump campaign event that Sessions and Kislyak attended.

The Justice Department has acknowledged that Sessions was at the Mayflower Hotel event in Washington, but said there were no private or side conversations that day.