The report in the Post was confirmation of a story that first appeared Monday in The Washington Times.
The information reportedly came from captured al-Qaida operations chief Khalid Sheik Mohammed, and may have involved "starting a fire."
"Law enforcement and intelligence sources said that Mohammed, the self-described architect of the Sept. 11, 2001, terrorist attacks, provided vague information about the plot along with plans to attack other U.S. targets at home and abroad," the Post said, "including the U.S. Capitol, and the Israeli Embassy in Washington."
Mohammed was captured March 1 in Pakistan.
During subsequent interrogation sessions, "Mohammed did not provide details about a terrorist strike on the Metro system, and authorities have been unable to determine whether there is any credible threat to mass transit here, two U.S. officials said yesterday," the Post said.
The officials said Mohammed may be providing truthful information, or may be trying to mislead U.S. intelligence.