Washington(CNN) Senators on the armed services committee are expected to receive a classified briefing from Pentagon officials Thursday on the Niger incident, according to two Senate sources.
The House armed services panel is also working to get a similar briefing for its members this week, according to a House source.
The anticipated briefings for lawmakers signals a more active role for Congress surrounding the circumstances of the Niger incident, in which four US service members were killed.
Senate Armed Services Chairman John McCain has criticized the Pentagon and Trump administration for not being forthcoming about the attack -- threatening a subpoena last week -- and Defense Secretary James Mattis went to Capitol Hill on Friday to meet with both McCain and South Carolina Republican Sen. Lindsey Graham.
"One of the fights I'm having with the administration is the armed services committee is not getting enough information," McCain said Monday on ABC's "The View." "We deserve it."
Both the House and Senate armed services committees have received staff-level briefings since the October 4 ambush. The House committee has been briefed six times, including notification on the day of the incident, according to one committee source. It's unclear how many staff briefings the Senate committee has received.
In the aftermath of the ambush, several key lawmakers have said they didn't know the US had troops in Niger. "I didn't know there was 1,000 troops in Niger," Graham said on NBC's "Meet the Press" Sunday.
But the Pentagon and White House have previously notified Congress about the US mission in Niger several times this year.
McCain pleads for unity in the wake of Niger attack
The White House sent a letter to Congress in June stating there were 645 US military personnel in Niger and 300 in Cameroon. And the head of Africa Command, Gen. Thomas Waldhauser, testified to the Senate armed services committee in March there were "approximately 1,000 personnel conducting 12 named operations across a nine-nation region."
The Senate briefing will come during a swirling political debate over the circumstances of the deaths of the soldiers.
One soldier, Sgt. La David Johnson, was separated from his 12-member team as it was ambushed by 50 ISIS fighters, and his body was recovered 48 hours later nearly a mile away from the central scene of the ambush in Niger, four administration officials familiar with the early assessment of what happened told CNN on Friday.