"According to many military experts, the idea of a quick withdrawal is not realistic; that [US forces] will be here for some time yet, and it will take a long time for Afghans to eventually defend themselves."
Ahmad Shah Ahmadzai, a former prime minister of Afghanistan, expressed disappointment with Obama's speech and his strategy.
"Sending more troops is not the solution to the Afghan crisis," he said.
"I was expecting Obama to announce the withdrawal of 30,000 troops within two months but unfortunately, he did the opposite which will increase killings of both Americans and Afghans."
And reacting to Obama's announcement by email, a Taliban spokesman told Al Jazeera that they were pleased with the decision to send more US soldiers.
"More troops just means a larger target for us to hit ... by increasing its forces in Afghanistan, Obama is just giving more power to the Mujahideen to recruit and receive the support of the civilian population."
Change of mission?
The new US deployment also fell short of a recommendation made by General Stanley McChrystal, the commander of US and Nato forces in Afghanistan, who had asked for 40,000 troops.
Al Jazeera's James Bays, reporting from the Afghan capital, Kabul, said: "This wasn't a counter-insurgency speech; it was a counter-terrorism speech, a very different mission from the one General Stanley McCrystal has been preparing himself for.
"He only mentions the Taliban twice in the whole speech. He started talking about 9/11, he ended with talking about 9/11 and all the references in between were to al-Qaeda."
Bays added: "I think there will be some in the military here in the command centre of Kabul who will be having to rethink things rather urgently."
However, after Tuesday's speech, McChrystal said that Obama's decision "has provided me with a clear military mission and the resources to accomplish our task".
The speech, which carries far-reaching strategic implications for the global effort to defeat the Taliban and al-Qaeda, also highlighted a stronger partnership with Pakistan to help to put down the insurgency in Afghanistan.
But Obama's orders received a cautious welcome from Pakistan.
"As far as Pakistan is concerned, Obama is offering the partnership, aid and lots of support and help," Ahmed Rashid, a Pakistani journalist and author, told Al Jazeera.
"But then again, it's the Pakistani military who will have to make very critical decisions as to whether it's going to help the Americans withdrawal and help bring the Taliban to the peace table."
Pakistan fears a US troop surge in Afghanistan would force fighters to flee to its border areas, particularly in the southwestern Baluchistan province where the government is already struggling to end a low-level insurgency by tribal fighters.
Rashid said: "But when Obama sent 20,000 marines into Afghanistan last March ... the opposite happened. What we've seen this summer is a massive escalation of attacks inside Afghanistan, the spread of the Taliban to the north and the west of the country for the first time."
Exit strategy concern
Pakistani officials are also nervously looking at Obama's exit strategy.
"Wars tend to consume presidencies and this is now Obama's war."
Bruce Riedel, a former CIA analyst
At a time when the Afghan government is struggling to take over security responsibilities, officials fear a hasty US pullout could trigger factional fighting in Afghanistan and lead to problems at home.
"The issue which is going to effect the region, and of course the Taliban and al-Qaeda very much is the president giving a date certain for the withdrawal of US troops," Rashid said.
"There's going to be a tendency among some of the Taliban leaders and al-Qaeda to sift out the Americans and think that the Americans are going to leave in 18 months, and then the country is ours. So how do you counter this idea amongst some of these extremists groups?"
Some Afghan officials expressed concern on Wednesday over Obama's aim to begin removing troops by 2011, saying that such a fixed timetable was not realistic.
Segbatullah Sanjar, the chief policy advisor for Hamid Karzai, the Afghan president, said: "We couldn't solve the Afghanistan problem in eight years, but now the US wants to solve it in eighteen months? I don't see how it could be done."
Officials also said that the talk of withdrawal of troops is premature and it could embolden the insurgency.
Bruce Riedel, a former CIA analyst, also added a note of caution, calling Obama's approach "shock therapy for Afghanistan."
"It is a bold approach and there's no guarantee of success," he said. "Wars tend to consume presidencies and this is now Obama's war."