As President George W. Bush pressed the case for war in Iraq in the summer of 2002, top State Department officials warned that an invasion to overthrow Saddam Hussein could spark internal Iraqi chaos, Middle East upheaval and threats to U.S. interests, according to formerly classified documents released this week.

“An effort to overthrow the regime in Baghdad could unravel if we’re not careful, intersecting to create a ’perfect storm’ for American interests,” three veteran diplomats with long experience in the Arab world wrote in a July 29, 2002, memo to Secretary of State Colin Powell. The White House ultimately ignored their warnings and the Bush administration invaded without detailed plans for post-war Iraq.

While the existence of the so-called “Perfect Storm” memo has been reported previously, its contents had been secret. The letter and more than 80 other formerly classified documents covering policy toward the Middle East, Russia and other regions were released in conjunction with the publication of “The Back Channel,” a memoir by former Deputy Secretary of State William Burns.

U.S. military forces invaded Iraq in March 2003, easily toppling Mr. Hussein’s regime but quickly finding themselves trapped in a bloody sectarian war. U.S. combat troops remained until 2011 and some returned in 2014 to help Iraq fend off a surging Islamic State.