Barack Obama on drone attacks
President Barack Obama gestures as he speaks about his administration's counter-terrorism policy at the National Defence University at Fort McNair in Washington - Reuters

President Barack Obama has asserted that drone attacks are a necessary evil to defend the US, but promised to limit the strikes in order to minimise civilian casualties.

In a rare public speech on targeted attacks on militants, Obama said drones are being used as a first strike option.

"America is at a crossroads" in tacking militants across the world, the President said. Apparently referring to al-Qaida, he added: "We are at war with an organisation that right now would kill as many Americans as they could if we did not stop them first."

At the same time, speaking at the National Defence University in Washington, he struck a note of caution: "And yet as our fight enters a new phase, America's legitimate claim of self-defence cannot be the end of the discussion. To say a military tactic is legal, or even effective, is not to say it is wise or moral in every instance. For the same progress that gives us the technology to strike half a world away also demands the discipline to constrain that power -- or risk abusing it."

Obama also proposed special courts to keep a check on targeted assassinations, which are often controversial and criticised by human rights groups. This is to end the perception of "boundless war on terror", he said.

At present the president needs to personally approve targeted drone strikes, but the latest proposal is expected to give some sort of legal sanction for the attacks.

The US is already finding it difficult to cope with the fallout of waging wars in Iraq and Afghanistan, which has taken a heavy toll on the country's economy. Large numbers of Americans are increasingly concerned with domestic healthcare and the economy.

Yet Obama sounded a warning over the threat posed by terrorism. "Our nation is still threatened by terrorists. We must recognise, however, that the threat has shifted and evolved from the one that came to our shores on 9/11."

Guantanamo Prison

Obama also took the opportunity to address the closure of the contentious Guantanamo Bay prison, which was one of the top priorities during his first term.

He announced that the current ban on the transfer of Guantanamo Bay inmates to Yemen will soon be lifted, prompting sharp reaction from Republicans.

Soon after Obama's speech, Republican Senator Saxby Chambliss told reporters: "We've got 166 of the meanest, nastiest killers in the world located at Guantanamo Bay today. If we were to transfer them to Yemen, it would be just like turning them loose. We should try those individuals at Guantanamo in the courtrooms and then make a decision about what to do with them."