The White House's national security adviser said Wednesday that he had already scheduled a classified meeting with congressional leadership before a top House Republican requested that President Joe Biden "declassify all information" that relates to "serious national security threat."

Two sources familiar with deliberations on Capitol Hill said the intelligence has to do with the Russians wanting to put a nuclear weapon into space.

This is not to drop a nuclear weapon onto Earth but rather to possibly use against satellites.

"It is very concerning and very sensitive," said one source, who called it "a big deal." While not addressing the subject matter directly, multiple members of Congress have described the issue as serious -- but nothing that should cause public alarm.

Jake Sullivan, the national security adviser, was pressed several times by reporters at a White House briefing about the Republican intelligence request, but he declined to specifically say if Thursday's meeting will be to discuss that reported threat.

He also declined to provide further details about it beyond saying that, broadly, "Americans understand that there are a range of threats and challenges in the world that we are dealing with every single day," such as terrorism.

"i am confident that President Biden, in the decisions that he is taking, is going to ensure the security of the American people," Sullivan said.

Earlier on Wednesday, Rep. Mike Turner, the chairman of the House Intelligence Committee, said in a statement that his panel had "made available to all Members of Congress information concerning a serious national security threat."

"I am requesting that President Biden declassify all information relating to this threat so that Congress, the Administration, and our allies can openly discuss the actions necessary to respond to this threat," Turner, an Ohio Republican, said.

A letter sent to members of Congress from the two top lawmakers on the House Intelligence Committee, obtained by ABC News, indicated the threat is linked to "a destabilizing foreign military capability that should be known by all Congressional Policy Makers."

Turner, the intelligence chair, said he's making information on the matter available in a secure location to all members of the House in accordance with chamber rules. Sullivan said at the White House briefing on Wednesday that he planned to meet with lawmakers.

"I reached out earlier this week to the Gang of Eight" -- referring to the leaders of both parties in both chambers of Congress and the ranking intelligence members -- "to offer myself up for a personal briefing ... and in fact we scheduled a briefing for the four House members of the Gang of Eight tomorrow," he said.

"So I am a bit surprised that Congressman Turner came out today," he said, stressing that he was looking forward to the Thursday meeting.

He also said the White House has "has gone further and in more creative, more strategic ways dealt with the declassification of intelligence in the national interest of the United States than any administration in history. So you definitely are not going to find an unwillingness to do that."

"But just to be clear, Turner calls it an urgent matter with regard to a destabilizing foreign military capability," ABC News Chief White House Correspondent Mary Bruce asked. "Are you aware that there is an emerging serious threat here that he's referring to?"

"'I'll just say that I personally reached out to the Gang of Eight. It is highly unusual, in fact, for the national security adviser to do that. I did that to set up a meeting. ... We'll have that conversation tomorrow," Sullivan said. "I'm not gonna say anything further."