The Biden-Harris administration is investigating a “deadly serious breach” of classified U.S. intelligence detailing Israeli plans for a strike on Iran, the latest in a series of targeted leaks against Israel that has put America’s closest Middle East ally on edge, according to current and former U.S. officials.

The explosive weekend release included top-secret Pentagon documents purporting to show Israel’s preparations for a large-scale counterstrike on Iran. The two documents—compiled by the National Geospatial-Intelligence Agency and National Security Agency over the past several weeks—expose how Israel is preparing for the attack, including the types of aircraft and munitions that are expected to be used. They were published by the Middle East Spectator, a little-known outlet that is known to disseminate propaganda from Tehran.

While the documents, according to CNN, include markings that indicate they were meant to be shared with the “Five Eyes” intelligence network—made up of the United States, United Kingdom, Australia, New Zealand, and Canada—a former U.S. intelligence community official who reviewed them said there is no question they emanated from the U.S. side. The documents, the former official said, appear to have been posted on a U.S. classified system that can be accessed by “thousands upon thousands” of American officials from across the government.”