"I will never hesitate to use force to protect the American people or our vital interests, I also promise you this - and this is very important as we consider our next steps in Afghanistan," Barack Obama said at a naval air station in Jacksonville on Monday.
"I will never rush the solemn decision of sending you into harm's way ... I won't risk your lives unless it is absolutely necessary, and if it is necessary, we will back you up.
Obama's address came hours after he led a sixth meeting of a bipartisan war council, which focused on future military strategy in Afghanistan.
The US president is considering whether to agree to a reported request by the senior commander of US and Nato forces in Afghanistan to have 40,000 more US troops sent to the country to crack down on resurgent fighters linked to the Taliban and al-Qaeda.
Obama is set to announce his decision on strategy "in the coming weeks", Robert Gibbs, the White House spokesman, said after the war council meeting on Monday.Critics of the president have accused him of taking too long to consider which direction he wants to take in the US battle in Afghanistan.
Dick Cheney, a former US vice-president, said last week that Obama was "dithering" and "waffling" over strategy, claims dismissed by the White House.
But John Kerry, a US senator who played a key role in brokering the run-off presidential election in Afghanistan between Hamid Karzai and Abdullah Abdullah, said that McChrystal's request contained risks.
"[McChrystal] understands the necessity of conducting a smart counterinsurgency in a limited geographic area. But I believe his current plan reaches too far, too fast," Kerry said.
"We do not yet have the critical guarantees of governance and of development capacity, the other two legs of counter-insurgency," Kerry told the Council on Foreign Relations in Washington.
Spencer Ackerman, a senior reporter with the Washington Independent, said that Kerry now has "a tremendous amount of prestige after brokering Hamid Karzai's agreement to run in the runoff election".
"He has quite a great amount of sway - his call today was basically to do a version of McChrystal's strategy, focusing on counter-insurgency in southern and eastern Afghanistan. He says he would only go for more American troops only if there are enough Afghan and US civilian capacity to build on the gains that the troops make."
During his address at Jacksonville, Obama paid tribute to 14 American service personnel killed in two helicopter crashes in Afghanistan on Monday."Our prayers are with these service members, their civilian colleagues and the families who loved them," Obama said.
"While no words can ease the ache in their hearts today, may they find some comfort in knowing this: like all those who give their lives in service to America, they were doing their duty and they were doing this nation proud."
Ten Americans were killed and 26 others were hurt when one helicopter crashed in western Afghanistan on Monday, security officials said.
A spokesperson for the Nato military alliance said the reason for the crash was "unconfirmed", ruling out hostile fire.
Another four US service members were killed and two others were wounded in an apparent mid-air collision between two helicopters in southern Afghanistan, Nato said in an earlier statement.
Colonel Wayne Shanks, from the US Army, said that investigations into both incidents were being hampered by "combat conditions".
"This is where we see the nexus between the insurgency and the narcotics trade," he said, adding that a dozen Taliban fighters were killed in the operation carried out by the helicopter brigade in the west of the country.
Nato and US troops are suffering the highest fatality rates since the deployment of foreign troops to Afghanistan in 2001. So far in October, more than 30 US soldiers have died.
Source: Al Jazeera (English)