The war on terror is not an endless conflict and the U.S. is approaching a "tipping point" after which the military fight against al-Qaida will be replaced by a law enforcement and intelligence operation, the Pentagon's top lawyer has said.

Jeh Johnson told an audience at Oxford University that the core of al-Qaida is "degraded, disorganized and on the run," according to a transcript of Friday's speech.

Johnson, general counsel to the U.S. Defense Department, said that once most al-Qaida members are captured or killed, armed conflict would be replaced by "a counterterrorism effort against individuals" led by law enforcement and intelligence agencies.

His speech to the Oxford Union debating society marked rare public comments by a senior U.S. official about the end of the armed conflict launched after the Sept. 11 attacks.

Shortly after 9/11, U.S. legislators passed a law that essentially granted the White House open-ended authority for armed action against al-Qaida.

Despite a promise to close the Guantanamo Bay prison camp for terror suspects, President Barack Obama has largely carried forward the anti-terrorism policies of his predecessor, George W. Bush. He authorized the raid that killed al-Qaida leader Osama bin Laden and has expanded the use of unmanned drone strikes against targets in Pakistan and Yemen.