GOP warning of 'national security threat' is about Russia wanting nuclear weapon in space: Sources

President Joe Biden's national security adviser and leading lawmakers on Capitol Hill sought to allay public concerns on Wednesday after the House Intelligence Committee chairman warned of a "national security threat" related to a "destabilizing foreign military capability" so serious that Biden should declassify "all information" about it.

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

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

Still, "it is very concerning and very sensitive," said one source, calling it "a big deal."

While not addressing the subject directly, multiple members of Congress quickly described the issue as serious without stoking public alarm.

"We are going to work together to address this matter, as we do all sensitive matters that are classified," House Speaker Mike Johnson told reporters at the Capitol on Wednesday afternoon.

"But we just want to assure everyone steady hands are at the wheel," he said.

Rep. Jim Himes, a Connecticut Democrat and the ranking member on the House Intelligence Committee, echoed that in his own statement, calling the warning "significant" but "not a cause for panic."

"As to whether more can be declassified about this issue, that is a worthwhile discussion but it is not a discussion to be had in public," Himes said.

Earlier on Wednesday, Ohio Republican 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 said.

He said he was making information on the matter available in a secure location to all members of the House in accordance with chamber rules.

Lawmakers arrived to the committee space throughout the afternoon to view the raw intelligence for Turner's warning, inside a secure facility in the basement at the Capitol.

"It's concerning," Rep. Bruce Westerman, R-Ark., said afterward, though he didn't address any additional details.

A letter sent to members of Congress from Turner and Himes, obtained by ABC News, indicated the threat is linked to "a destabilizing foreign military capability that should be known by all Congressional Policy Makers."

The White House's national security adviser, Jake Sullivan said at Wednesday's press briefing that he had already scheduled a classified meeting with congressional leadership before Turner's request.

Sullivan was pressed several times by reporters about the intelligence request, but he declined to specifically say if Thursday's meeting will be to discuss the 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.

"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. (Turner repeatedly declined to comment further to ABC News.)

Sullivan said that 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," Sullivan responded.

President Biden had been tracking the threat cited by Turner and specifically asked Sullivan to "engage" the Gang of Eight on it, a U.S. official confirmed to ABC News.

"I did that to set up a meeting. ... We'll have that conversation tomorrow," Sullivan said at the briefing. "I'm not gonna say anything further."

ABC News' Mary Bruce, Fritz Farrow and Lauren Peller contributed to this report.