President Barack Obama ordered all 33,000 US surge troops home from Afghanistan by next summer, declared the beginning of the end of the war and vowed to turn to "nation building" at home.

US soldiers from Viper Company (Bravo), 1-26 Infantry, are pictured during a patrol at Combat Outpost (COP) Sabari in Khost province in the east of Afghanistan.

In a pivotal moment for US national security strategy, Obama also signaled in a 13-minute primetime speech on Wednesday that the United States would no longer try to build a "perfect" Afghanistan from a nation ravaged by generations of violence.

"Tonight, we take comfort in knowing that the tide of war is receding," Obama said in the East Room of the White House in an address blanketing US television networks at a time of rising discontent on the war.

"Even as there will be dark days ahead in Afghanistan, the light of a secure peace can be seen in the distance. These long wars will come to a responsible end," Obama said.

The president\'s speech came as domestic political support fades for the war following the killing of Al-Qaeda chief Osama bin Laden by Navy SEALS, and as Washington backs fragile Afghan reconciliation talks with the Taliban.

His decision on troop numbers amounted to a rejection of appeals from the Pentagon for a slower drawdown to safeguard gains against the Taliban and to allow a new counter-insurgency mission to unfold in eastern Afghanistan.

The president said that he would, as promised, begin the US withdrawal this July and that 10,000 of the more than 30,000 troops he sent to war in an escalation of the conflict in 2009 would be home this year.

A further 23,000 surge troops will be withdrawn by next summer, and more yet-to-be announced drawdowns will continue, until Afghan forces assume security responsibility in 2014.

"This is the beginning -- but not the end -- of our effort to wind down this war," Obama said.

"We will have to do the hard work of keeping the gains that we have made, while we draw down our forces and transition responsibility for security to the Afghan government."

Though Obama said the tide of war was receding, there will still be more than 65,000 troops in Afghanistan when he asks Americans to give him a second term in November 2012.

Obama also argued that his policy of escalating the war against the Taliban and Al-Qaeda had forged substantial progress and had allowed him to commence troop withdrawals from a "position of strength."

He said that documents seized from bin Laden\'s compound in Pakistan showed that the Al-Qaeda organization was under "enormous strain."

"Bin Laden expressed concern that Al-Qaeda has been unable to effectively replace senior terrorists that have been killed, and that Al-Qaeda has failed in its effort to portray America as a nation at war with Islam -- thereby draining more widespread support," he said.

General David Petraeus and top Pentagon officials had asked for a slower drawdown through summer 2012 to allow them to solidify gains in southern Afghanistan and to mount counter-insurgency operations in eastern districts.

Senator John McCain, a hawkish Republican, said Obama\'s decision, represented an "unnecessary risk" and noted Petraeus and Defense Secretary Robert Gates had recommended a "more modest withdrawal."

But Obama\'s timetable may be too slow for critics who want faster withdrawals from a war launched 10 years ago to oust the Taliban after it offered Al-Qaeda a haven before and after the September 11 attacks in 2001.

Some of Obama\'s fellow Democrats and some Republicans are demanding a faster US exit from Afghanistan, and questioning the huge $10 billion a month cost of the conflict at a time of deep fiscal pain.

Obama argued the surge had made progress towards key objectives he laid down at the start of the escalation, namely: reversing Taliban momentum, disrupting and dismantling Al-Qaeda and building Afghan forces towards an eventual assumption of security duties.

One official said the US operation against Al-Qaeda in Afghanistan and Pakistan tribal regions had "exceeded our expectations," saying 20 of the group\'s top 30 leaders, including bin Laden had been killed in the last year.

Administration aides also rejected criticism that Obama\'s decision would put recent gains in danger and increase the chances that Afghanistan will slip back into an abyss of deep violence.

Obama also placed the Afghan mission in the context of his wider foreign policy and war strategy, arguing he has drawn down 100,000 troops from Iraq and will oversee the promised full withdrawal by the end of this year.

He announced that a NATO summit to review progress on Afghanistan will take place in his hometown of Chicago in May 2012, alongside the G8 summit of industrialized nations.