President Barack Obama defends US drone strikes - but moves to rein them in as Guantanamo Bay closure rears its head again

President Barack Obama combined a vigorous defence of his controversial use of drones with a no less impassioned demand for the closure of the notorious prison at Guantanamo Bay, Cuba, which he called “a symbol around the world for an America that flouts the rule of law.”

In a sweeping public reassessment of the evolving threat facing the US, Mr Obama directly addressed two of the most controversial aspects of the country's "war on terror": the use of armed unmanned drones to pre-emptively kill suspected militants thousands of miles from America's borders; and the future of Gitmo, where some inmates have been held without charge or trial for more than 11 years.

On drones, Mr Obama argued that such attacks were not only legal, but that they were the most efficient and least bloody means of going after terrorists who posed an imminent danger, in remote and lawless places beyond the reach of government. Drones had caused "heartbreaking" civilian casualties, he admitted, but they were safer than the alternatives, when an armed intervention by US troops on the ground could cause both more deaths among innocent civilians and also trigger an international crisis.

The President's remarks coincided with the issuance of a new "Presidential policy guidance" on drone strikes. Mr Obama conceded the need for greater oversight of their use. But he made no reference to reports that control of such operations is being gradually shifted from the paramilitary arm of the CIA to the more publicly accountable Pentagon. At times his speech turned into a review of the entire history of terrorism, as he argued that with al-Qa'ida's leadership broken and on the run, the pattern had reverted to the 1980s and 1990s, before 9/11 – since when there had been no significant terrorist attack on US soil.

The response now could not solely consist of military force and law enforcement, but had to tackle the root causes of the problem. "In the years to come, not every collection of thugs that labels themselves al-Qa'ida will pose a credible threat to the United States," Mr Obama said.

Whether the President's words will allay criticism at home is doubtful, not least on Capitol Hill where many – Democrats and Republicans alike – worry that the sweeping anti-terror measures passed in the wake of 9/11 give the White House unbridled powers to use military force anywhere in the world.

Nor are human rights groups likely to be satisfied. Dixon Osburn, legal director of Human Rights First, welcomed the pledge of greater transparency, but said he was "deeply concerned" that the White House "appears to be institutionalising a problematic targeted killing policy without public debate."

Preparing the ground for Mr Obama's address, his administration on Wednesday acknowledged for the first time that four US citizens have been killed by drone attacks, outside the formal battlefields of Afghanistan and Iraq. The deaths of three of them – the radical cleric Anwar al-Awlaki, his son and another militant – in a drone strike in Yemen 18 months ago were widely reported, but the killing of a fourth, Jude Kenan Mohammad, allegedly involved in a terrorist ring in North Carolina, was not previously known.

In a letter to Congress, the Attorney General, Eric Holder, argued that the Awlaki operation conformed to the principle that drone attacks were justified when the threat was imminent and where capture of the target was "not feasible". Awlaki was suspected of being behind the attempted bombing of an airliner near Detroit at Christmas 2009, among other charges.

In fact, drone strikes already appear to be declining in number, in part because of public complaints, in part because many top-tier terrorist targets are now dead. Even so, their use has markedly increased since Mr Obama took office.

On Gitmo, listeners broke out in spontaneous applause when a woman protester in the audience at the National Defence University at Fort McNair repeatedly interrupted him and denounced the facility – even as the President announced a series of steps towards shutting the prison.

These include the reappointment of a top-level State Department envoy to work on the transfer of inmates to their own countries, an end to the ban on repatriations of Yemenis, and renewed search for a site on the US mainland.

"Her voice is worth listening to," the President said, after he heard the protester out, almost seeming to agree with her, "these are tough issues, they cannot be glossed over."