WASHINGTON, May 23: President Barack Obama outlined plans on Thursday to limit the use of US drone strikes against extremists abroad and took steps aimed at breaking a deadlock on closing the Guantanamo Bay military prison.

In a major foreign policy speech after two weeks of fending off domestic scandals, Mr Obama limited the scope of what his predecessor, George W. Bush, had called a global war on terror after the Sept 11, 2001 attacks.

“Our nation is still threatened by terrorists,” he said at Washington’s National Defence University. “We must recognise however, that the threat has shifted and evolved from the one that came to our shores on 9/11.”

Faced with criticism about the morality of using unmanned aerial vehicles to wage war in distant lands, Mr Obama said the United States would only use drone strikes when a threat was imminent, a nuanced change from the previous policy of launching strikes against a significant threat.

“To say a military tactic is legal, or even effective, is not to say it is wise or moral in every instance,” he said. Under a new presidential guidance signed on Wednesday, Mr Obama said the Defence Department would take the lead in launching drones, as opposed to the current practice of the CIA taking charge.

Any drone strike will only be launched when a terrorism suspect cannot be captured. The United States will respect state sovereignty and will limit strikes to Al Qaeda or associated targets, he said.

“And before any strike is taken, there must be near-certainty that no civilians will be killed or injured — the highest standard we can set,” said Mr Obama. The use by the United States of armed drone aircraft to attack extremists has increased tensions with countries such as Pakistan and drawn criticism from human rights activists. President Obama acted in line with a promise to be more open about the issue.

Mr Obama has faced pressure from both supporters and opponents to allow greater scrutiny of the secretive decision-making process guiding drone use. He said earlier this year he wanted to be more open about the issue.

His policy shift came after the Obama administration acknowledged on Wednesday that four Americans abroad had been killed in drone strikes since 2009 in counter-terrorism operations in Yemen and Pakistan, including militant cleric Anwar al-Awlaki.

President Obama defended those operations, saying when a US citizen goes abroad to wage war against the United States, his citizenship should not be a shield. But in recognition of a debate within Congress about whether strikes could be launched within the US, he said it would not be constitutional to do so.—Reuters