He said the US was mindful of Pakistani sovereignty but said the US could not allow "active plans to come to fruition without us taking some action".

The killing of Bin Laden by US forces in a Pakistani garrison town on 2 May strained ties between the two allies.

President Barack Obama was speaking to the BBC ahead of a European visit.

Asked what he would do if one of al-Qaeda's top leaders, or the Taliban leader Mullah Omar, was tracked down to a location in Pakistan or another sovereign territory, he said the US would take unilateral action if required.

"Our job is to secure the United States," he told the BBC's Andrew Marr during a wide-ranging interview.

"We are very respectful of the sovereignty of Pakistan. But we cannot allow someone who is actively planning to kill our people or our allies' people.

"We can't allow those kind of active plans to come to fruition without us taking some action."