President Trump revealed highly classified information to the Russian foreign minister and ambassador in a White House meeting last week, according to current and former U.S. officials, who said Trump’s disclosures jeopardized a critical source of intelligence on the Islamic State.

The information the president relayed had been provided by a U.S. partner through an intelligence-sharing arrangement considered so sensitive that details have been withheld from allies and tightly restricted even within the U.S. government, officials said.

The partner had not given the United States permission to share the material with Russia, and officials said Trump’s decision to do so endangers cooperation from an ally that has access to the inner workings of the Islamic State. After Trump’s meeting, senior White House officials took steps to contain the damage, placing calls to the CIA and the National Security Agency.

“This is code-word information,” said a U.S. official familiar with the matter, using terminology that refers to one of the highest classification levels used by American spy agencies. Trump “revealed more information to the Russian ambassador than we have shared with our own allies.”