U.S. Defense Secretary Lloyd Austin said on Tuesday that the United States is taking the alleged leak of classified intelligence documents "very seriously."

The secretary made the remarks in a press conference with U.S. Secretary of State Antony Blinken following talks with their Philippine counterparts in Washington.

Pledging to continue working closely with U.S. allies and partners, Austin said nothing will ever stop the U.S. from maintaining its security.

The U.S. defense chief said that he was first briefed about the unauthorized disclosure of sensitive and classified material on the morning of April 6, and has since convened with senior department leaders daily.

Austin said that he ordered an urgent inter-departmental effort and the Pentagon has referred the matter to the Department of Justice, which has opened a criminal investigation.

He went on to say that the documents that the Defense Department is aware of were dated February 28 and March 1, and vowed to conduct a comprehensive investigation to discover the source and extent of the leak.