"The situation in Afghanistan has deteriorated," Obama said. "Our new commander in Afghanistan -- General (Stanley) McChrystal -- has reported that the security situation is more serious than he anticipated. In short: The status quo is not sustainable," he said.

In his 35-minute prime-time national address, he sought to convince an increasingly sceptical nation that resurgence of Taliban in Afghanistan and continued existence of al-Qaeda across the border in Pakistan were direct threats to the US.

"America -- we are passing through a time of great trial. And the message that we send in the midst of these storms must be clear: that our cause is just, our resolve unwavering," Obama, also the Commander-in-Chief of the US military, said at the elite US Military Academy, West Point in New York.

"Our new approach in Afghanistan is likely to cost us roughly USD 30 billion for the military this year, and I'll work closely with Congress to address these costs as we work to bring down our deficit," the US President said.