If conditions are right, Mr. Obama said U.S. forces could begin leaving Afghanistan in 18 months. Gen. Stanley McChrystal, the top U.S. commander in the country, said the Afghan government and its international partners should use the coming year-and-a-half to convince the Taliban they can't win and offer militants a way to quit the insurgency "with dignity."
In a statement, the Taliban said the Obama administration's plan was "no solution for the problems of Afghanistan" and would give insurgents an opportunity "to increase their attacks and shake the American economy, which is already facing crisis."
Mr. Obama only set a tentative pullout date for July 2011 to lessen the sensitivities of Afghans about the troop buildup and decrease the American public's opposition to the war, the Taliban statement said.
"This stratagem will not pay off," it said, adding the surge will result in increased deaths of U.S. troops.
More than 850 members of the U.S. military have died in Afghanistan, Pakistan and Uzbekistan as a result of the U.S. invasion of Afghanistan in late 2001, according to the Defense Department. Of those, the military reports nearly 660 were killed by hostile action.
NATO reported the latest U.S. service member was killed in eastern Afghanistan on Tuesday when his patrol was attacked by insurgents.
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In a speech to troops in the southern city of Kandahar, Gen. McChrystal said the main thrust of the new strategy will focus on Afghanistan's volatile south, where the Taliban's influence is strongest.
"This (war) will go on for quite awhile, but it will be decided, in my view, in the next one or two years," McChrystal said. "I believe that by this time next year we'll see a level of progress."
The Afghan government welcomed Mr. Obama's announcement but cautioned against setting a deadline for handing over security to Afghan forces and starting to withdraw.
Reaction among Afghans and U.S. soldiers was mixed, with many wondering whether the Afghan government can meet the challenges of fighting both corruption and the insurgents, and whether the surge means more Afghan civilians will die.
"I am asking America 'What did you do for the last eight years against your enemies? You have killed Afghans and your enemies have killed Afghans. It seems you are weak and the enemy is strong. Will you defeat the enemy this time?" said Haji Anwar Khan, a white-bearded resident of Kandahar.
Shortly after Mr. Obama's speech, McChrystal told reporters the 18-month timetable was enough time to build up Afghan forces and convince the people of this war-ravaged country that they can eventually take care of their own security.
He said the Afghan government and the coalition should also use that period "to convince the Taliban and the people from whom they recruit that they cannot win - that there is not a way for the insurgency to win militarily."
At the same time, he said the U.S. should support the Afghan government in reintegrating militants.
"I think they should be faced with the option to come back if they are willing to come back under the constitution of Afghanistan - that they can come back with dignity," he said. "If you look at the end of most civil wars and insurgencies, I think that everybody needs a chance to come back with dignity and respect and rejoin society. I think that will be important for us to look forward to."
McChrystal said he met Wednesday with President Hamid Karzai for nearly an hour and described the Afghan leader's reaction as "really positive."
"The president was very upbeat, very resolute this morning," he said. "I really believe that everybody's got a focus now that's sharper than it was 24 hours ago."
But Interior Minister Hanif Atmar said the 18-month timeframe was too short for a complete handoff from international forces.
"We are hoping that there will be clarity in terms of long-term growth needs of the Afghan national security forces and what can be achieved in 18 months," Atmar said.
In neighboring Pakistan, Mr. Obama's speech drew a lukewarm reaction. Key al Qaeda leaders including Osama bin Laden are believed to have taken refuge in Pakistan, and Mr. Obama's announcement of a tentative date to begin withdrawing U.S. troops could deter Islamabad from cracking down on Taliban fighters using Pakistani territory as a safe haven.
"The Americans would like to keep the pressure on the Pakistan army to chase the militants all over the tribal regions, but Pakistan of course has to see whether it's feasible," said Dr. Riffat Hussain, a professor of Defense Studies at Quaid-e-Azam University in Islamabad. "It seems Pakistan prefers the incremental approach."
In Brussels, NATO Secretary-General Anders Fogh Rasmussen said he expects the allies to boost the NATO-led force by more than 5,000 soldiers. He said the best way to overcome widespread public opposition to the war in Europe is by demonstrating progress on the battlefield.
Capt. Mark Reel from Norfolk, Virginia, U.S. military civil affairs officer deployed in Wardak province, west of Kabul, said more troops mean nothing unless they can give local Afghans a sense of security.
"They have to believe they are more secure. You get thousands of troops on some of these bases here, but what are they really doing? The troops just have to get out there." The reason the surge worked in Iraq, he said, is because troops were able to get into the field and make Iraqis feel safer.
Davood Moradian, senior adviser to the Afghan Ministry of Foreign Affairs, welcomed Mr. Obama's statement but cautioned against comparing the wars in Afghanistan and Iraq.
"We are very pleased and support President Obama's analysis that Afghanistan is not Vietnam. But I think Afghanistan is not Iraq. Therefore, we have to be very careful about that," he said.
Ghulam Haider Hamidi, the mayor of Kandahar, cited corruption as the worst problem facing his nation.
"The biggest problem is corruption in the Afghan government, police and military but also in some of the companies coming from the United States, Canada and England and Germany," Hamidi said. "There is corruption and drug dealing by the people who are in power, within the police and the military."
Hamidi said just last month he was told that Taliban were sleeping in the police barracks.
"The police are taking money from both sides - the government and the Taliban," he said. "When we have this kind of police and military, the Afghan problem won't be solved in 20 years."
He also said safe havens next door in Pakistan have to be shut down if Afghanistan's insurgency is to be curbed. On Wednesday, a suicide attacker struck Pakistan's naval headquarters in Islamabad, which has been hit by a series of bombings in recent months by Islamist militants.
"More American troops will mean more violence," said Pakistani engineering student Ammar Ahmed, 20. "It will worsen the situation both in Afghanistan and Pakistan."