Contradicting Pakistan President Asif Ali Zardari's [Images] claims, United States President Barack Obama [Images] has suggested that Osama bin Laden [Images] is still alive and he is operating under the assumption that the Al Qaeda [Images] leader is not dead.

Addressing a town hall meeting in the central state of Missouri, the US President also reiterated his administration's position that Al-Qaeda [Images] and the Taliban [Images] "are the single most direct threat to our national security interests."

"As commander-in-chief, it is my responsibility to make sure that bin Laden and his cronies are not able to create a safe haven within which they can kill another 3,000 Americans or more," Obama said in an apparent reference to those killed in the September 11, 2001 attacks.

"That's an obligation that I have," he said.

Earlier this week, Zardari had said that Osama might be dead but had no evidence.

"The Americans tell me they don't know, and they are much more equipped than us to trace him. And our own intelligence services obviously think that he does not exist any more, that he is dead," he said.

The fate of Osama has been a subject matter of intense speculation even as the US makes all out efforts to trace one of the world's wanted terrorists.

Obama also defended his decision to send thousands of more troops to Afghanistan to fight the insurgency despite objections from fellow Democrats.