WASHINGTON — In the months leading up to the Sept. 11 attacks on the US diplomatic mission in Benghazi, the Obama administration received intelligence reports that Islamic extremist groups were operating training camps in the mountains near the Libyan city and that some of the fighters were ‘‘Al Qaeda-leaning,’’ according to US and European officials.

The warning was part of a stream of diplomatic and intelligence reports that indicated that the security situation throughout the country, particularly in eastern Libya, had deteriorated sharply since the United States reopened its embassy in Tripoli after the fall of Moammar Khadafy’s government in September 2011.