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."