U.S. President Barack Obama laid out new guidelines for drone strikes on Thursday and launched a new bid to close Guantanamo Bay, warning that a “perpetual” U.S. war on terror would be self defeating, AFP reports.

Obama told Americans their country was at a crossroads and must move on from the counter-terrorism policies deployed after the September 11 attacks to confront a new era of diverse global threats and homegrown radicals.

He argued that the idea of using military might in a “boundless” war everywhere that radicalism took root, be it in Pakistan or Arab Spring nations or Somalia, was now obsolete.

“A perpetual war — through drones or Special Forces or troop deployments — will prove self-defeating, and alter our country in troubling ways,” he said, seeking to shape his second term and own political legacy in a major speech, according to AFP.

“We must define the nature and scope of this struggle, or else it will define us,” Obama said, warning that some post 9/11 tactics like enhanced interrogation of terror suspects had “compromised our basic values.”

But Obama also mounted a firm defense of his covert drone war as legal and just and the best way to confront terrorism plots against Americans, though warned that undisciplined use of the tactic would invite abuses of power.

He said he had signed a new policy directive codifying guidelines for the use of U.S. drone strikes because “to say a military tactic is legal, or even effective, is not to say it is wise or moral in every instance.”

The guidelines state that drone attacks can only be used to prevent imminent attacks and when the capture of a suspect is not feasible and if there is a “near certainty” that civilians will not be killed.

The rules would follow the same criteria as those used for attacks on U.S. citizens who have aligned themselves with foreign terror groups.

Such criteria, however, would still give the administration wide discretion to use a covert strategy condemned by some rights groups and civil libertarians.

On Wednesday, the administration admitted for the first time that it had killed Yemeni-American cleric Anwar al-Awlaki in a drone strike in Yemen in 2011, and that three other U.S. citizens also died in anti-terror strikes abroad.

Obama, in the speech at the National Defense University, said that he would be “haunted” for the rest of his life by the deaths of civilians in strikes he had ordered — but had no choice but to act when Americans were at risk.

He said, however, his policies had been successful in neutralizing the threat of action from core Al-Qaeda leaders in Afghanistan and Pakistan, though cautioned the raid that killed Osama bin Laden was too risky to become the norm.

Obama also signaled a major new effort to close the Guantanamo Bay camp for terror suspects in Cuba, which he billed as harmful to U.S. interests, too expensive and a relic of a past age of counterterrorism tactics.

He pledged to lift a personal moratorium on transferring Guantanamo Bay inmates to unstable Yemen and promised to appoint a senior envoy to work in the State Department and Pentagon to oversee transfers. Yemen welcomed the announcements.

He also called on the Pentagon to designate a site on U.S. soil to hold military tribunals for terror suspects now at Guantanamo Bay, and said Congress must now drop efforts to thwart his closure plans.

“I know the politics are hard. But history will cast a harsh judgment on this aspect of our fight against terrorism and those of us who fail to end it,” Obama said, according to AFP.

Obama offered no solution for inmates deemed too dangerous for release but who cannot be tried because evidence against them was obtained through coercion and may not be admissible in court.

He also called on Congress to amend the legal authorization for U.S. anti-terror operations, adopted in the aftermath of the September 11 attacks, saying it did not reflect the evolved threat.

“Not every collection of thugs that label themselves Al-Qaeda will pose a credible threat to the United States,” he said, according to AFP.

“Unless we discipline our thinking and our actions, we may be drawn into more wars we don’t need to fight.”