WASHINGTON (AP) — The Republican head of the House Intelligence Committee urged the Biden administration on Wednesday to declassify information about what he called a serious national security threat.

Rep. Mike Turner gave no details about the nature of the threat, and the Biden administration also declined to address it. But several leading lawmakers, including House Speaker Mike Johnson, cautioned against being overly alarmed.

Johnson said he was not at liberty to disclose the classified information. "But we just want to assure everyone steady hands are at the wheel. We're working on it and there's no need for alarm," he told reporters at the Capitol.

Turner earlier Wednesday sent an email to members of Congress saying his committee had "identified an urgent matter with regard to a destabilizing foreign military capability" that should be known to all congressional policy makers. He encouraged them to come to a SCIF, a secure area, to review the intelligence.

Turner has been a voice for stronger U.S. national security, putting him at odds with some Republican colleagues who favor a more isolationist approach. He has called for the renewal of a key U.S. government surveillance tool while some fellow Republicans and liberal Democrats have raised privacy objections.

And he supports continuing U.S. military aid for Ukraine in its war against Russia at a time that the funding remains uncertain because of opposition in the Republican-led House.

Democratic Rep. Jim Himes, the ranking member of the Intelligence Committee, said in a statement that the classified information is "significant" but "not a cause for panic."

The Senate Intelligence Committee said it has been tracking the issue.

"We continue to take this matter seriously and are discussing an appropriate response with the administration," Sen. Mark Warner, the Democratic committee chairman, and Sen. Marco Rubio, the Republican vice chairman, said in a statement. "In the meantime, we must be cautious about potentially disclosing sources and methods that may be key to preserving a range of options for U.S. action."

Turner's announcement appeared to catch the Biden administration off-guard.

National security adviser Jake Sullivan told reporters at the White House that he already had been due to brief Turner and other senior congressional leaders on Thursday. Sullivan did not disclose the topic or provide any other details related to Turner's statement.

"I'm focused on going to see him, sit with him as well as the other House members of the Gang of Eight, tomorrow," Sullivan said. "And I'm not in a position to say anything further from this podium at this time."

He acknowledged it was not standard practice to offer such a briefing.

"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 said. He said he had reached out earlier this week.

Johnson said he sent a letter last month to the White House requesting a meeting with the president to discuss "the serious national security issue that is classified." He said Sullivan's meeting was in response to his request.

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Associated Press writers Aamer Madhani and Kevin Freking contributed.