WEST POINT: President Barack Obama announced a 30,000 strong troop surge to "seize the initiative" in Afghanistan and finally end the brutal eight-year war.

"As commander in chief, I have determined that it is in our vital national interests to send an additional 30,000 troops to Afghanistan," Obama said, but offered an immediate signal the US mission was not open ended.

"After 18 months, our troops will begin to come home."

In a major televised address, Obama placed a major political and military bet that a fast influx of troops could defeat Al-Qaeda, crush a resurgent Taliban and pave a way home for US forces after years of bloodshed.

He upped pressure on NATO allies to match his action in getting all new soldiers into action within six months with more troops.

In a speech targeting multiple audiences at home and abroad, Obama also rejected dire parallels between the Afghan war which haunts his presidency, and a Vietnam-style quagmire.

"Afghanistan is not lost, but for several years, it has moved backwards," Obama said, saying the new troops would be raced to the battlefield. For the first time he set a deadline for the start of a drawdown of all US forces. Related article: NATO, US troop numbers in Afghanistan

But Obama did not establish a deadline for the US mission to end. Officials said separately that the pace of the withdrawal and the eventual full exit strategy would depend on conditions on the ground.

The speech at the US Military Academy at West Point marked the biggest leadership test yet for Obama, designed to quell fears the war may consume the reforming promise of his presidency.

Following an exhaustive strategy review, Obama rolled out new approaches to the Afghan war and Pakistan and vowed to redouble the US battle against Al-Qaeda wherever it emerged.

The top US and NATO military commander in Afghanistan hailed Obama's new strategy for the war and said his "main focus" now will be to build up Afghan security forces.

"The Afghanistan-Pakistan review led by the President has provided me with a clear military mission and the resources to accomplish our task," US Army General Stanley McChrystal said in a statement.

"The clarity, commitment and resolve outlined in the president?s address are critical steps toward bringing security to Afghanistan and eliminating terrorist safe havens that threaten regional and global security," he said.

McChrystal, who commands US forces in Afghanistan as well as NATO's International Security Assistance Force (ISAF), vowed to hand Afghan security forces fresh responsibility "as rapidly as conditions allow."

"In the meantime, our Afghan partners need the support of Coalition forces while we grow and develop the capacity of the Afghan army and police. That will be the main focus of our campaign in the months ahead," he said.

In simple, direct language, shorn of the rhetorical flourishes normally seen in his soaring speeches, Obama said he understood the human and financial costs of the war, but saw not choice but to escalate it.

Obama also vowed to "keep the pressure on Al-Qaeda" which used a safe-haven in Afghanistan to plot the September 11 attacks in 2001, which triggered the US war and grueling war on terror.

He cautioned that strikes against America were "being plotted as I speak," and said he would go after Osama bin Laden's terror group in Somalia or Yemen or further afield if necessary.

Obama also told the Afghan government of President Hamid Karzai, that the days of a US "blank check" were over, demanding efforts to combat corruption and to hold those who transgress accountable.

He said that the same "cancer" of extremism that had torn at Afghanistan, was also hurting Pakistan.

"We will act with the full recognition that our success in Afghanistan is inextricably linked to our partnership with Pakistan," Obama said, promising a foundation of "mutual interests, mutual respect and mutual trust" with Islamabad.

As many of Obama's Democratic allies balk at the cost of the new troop surge, Obama warned the new Afghan war operations would cost 30 billion dollars this year. Related article: Obama struggles with Afghan exit dilemma

But in a swipe at the former Bush administration, blamed for not paying for conflicts in Afghanistan and Iraq, he said he would be open and honest in financing the operation -- though he did not offer any firm commitments.

The president, in a clear call for more support from US allies, said the effort to successfully end the war launched after the September 11 attacks in 2001, was a test of NATO credibility and common global security efforts.

"Some have already provided additional troops, and we are confident that there will be further contributions in the days and weeks ahead," he said.

Despite Obama's call for more troops from US allies, France ruled out sending more combat troops, but said military trainers could be a possibility. Germany said it would not decide until after a London conference on Afghanistan on January 28.

Britain has already offered an extra 500 troops, Italy has said it will send an unspecified number, while Poland is considering deploying several hundred more soldiers.

Even with the US surge troops and more NATO soldiers, the deployment will fall short of the 40,000-strong extra forces requested by war commander General Stanley McChrystal when he warned the war could be lost without more soldiers.