US will 'turn over every rock' to find source of classified documents leak: Austin

Defense Secretary Lloyd Austin said Tuesday that the U.S. will "turn over every rock" to find the source of the apparent leak of dozens of highly classified documents on the internet in his first public comments since the documents came to light.

More apparently leaked documents continued to emerge on Monday as The Washington Post reported on documents it says it obtained that appear to raise concerns that Ukraine's upcoming spring offensive will only be moderately successful and that Egypt's leader had secretly directed that his country provide Russia with thousands of rockets.

"We take this very seriously and we will continue to investigate and turn over every rock until we find the source of this and the extent of it," Austin told reporters at a State Department press conference.

Austin told reporters that he was first informed of the apparent leak the morning on April 6 after some of the documents were posted on popular social media platforms. He said that since then he has been leading daily meetings with top officials to coordinate a response to the leak and directed "an urgent cross-department effort."

Austin said he was limited in what he could say because of the ongoing Justice Department criminal investigation into the leak but he provided new details that investigators are focused on documents dated Feb. 28 and March 1.

"I don't know if there are other documents that have been online before," he said. "These are things that we will find out as we continue to investigate."

"They were somewhere in the web and where exactly and who had access at that point, we don't know, we simply don't know at this point," he acknowledged.

An ABC News review has found that the first of what appear to be highly classified U.S. military and U.S. intelligence documents were posted on the chat website Discord on March 2. But they did not reach a wider audience until last Wednesday when some of the documents related to the war in Ukraine were posted on social media platforms.

The documents seem to contain top-secret intelligence about the war in Ukraine and other parts of the world that is made available daily to hundreds of U.S. officials in the U.S. and overseas via classified computer servers that can only be accessed with a top-secret clearance.

The Washington Post reported that one of the leaked documents it says it obtained was a U.S. intelligence assessment that Ukraine would make only modest gains to retake occupied territory from Russia in its upcoming spring offensive as it challenges to raise troops, ammunition and equipment.

That apparent assessment is in line with a separate classified U.S. intelligence assessment by the National Intelligence Council (NIC) that was recently briefed to Congress, according to a U.S. official.

Austin downplayed the idea that a public disclosure of Ukraine's challenges ahead of the offensive and said he had just spoken with Ukraine's Defense Minister Oleksii Reznikov.

"He and the leadership remain focused on the task at hand, and I have every confidence that they will do what good leaders, great leaders do," said Austin. "They will fight the enemy and not be driven by a specific plan. They have a great plan to start, but only President Zelenskyy and his leadership really know the full details of that plan."

"They have much of the capability that they need to continue to be successful," he added. "We trained an enormous number of troops, we provided a substantial number of platforms. And so, I think he feels that they're in a pretty good position."

The Washington Post also reported that it had obtained another document that indicated that Egypt's President al Sisi had apparently directed officials to secretly provide thousands of rockets to Russia.

Egyptian state media dismissed the report as "rumors" and John Kirby, the National Security Council's coordinator for strategic communications said "we've seen no indications that Egypt is providing lethal weaponry capabilities to Russia." ABC News has not seen either of the documents cited by The Washington Post.

The flow of documents has led top American officials to reach out to counterparts as the leaked documents seem to show that U.S. intelligence was not only spying on Russia and other adversaries but on its allies and partners, including Ukraine.

"We have engaged with allies and partners at high levels over the past the past days, including to reassure them about our own commitment to safeguarding intelligence and, of course, our commitment to our security partnerships," Secretary of State Antony Blinken said at the news conference as Austin that followed their meeting with their counterparts from the Philippines.

"We are determined to assist Ukraine in the efforts that it's making to regain the territory that's been seized from it, and I reaffirmed that commitment today in speaking to Foreign Minister Kuleba," Blinken said.

ABC News' Trish Turner and Matt Seyler contributed to this report.