The US military has dramatically stepped up air strikes and manhunts in Afghanistan in a bid to weaken the Taliban, reflecting a return to "counter-terrorism" tactics.

Dropping more bombs and carrying out more raids by special operations forces underscores a sense of urgency in the war effort, as the White House prepares to release a strategy review and commanders try to change the dynamic of a conflict mired in stalemate.

In announcing a surge of 30,000 troops a year ago, President Barack Obama embraced the idea of a "counter-insurgency" strategy that focused less on firefights with the Taliban and more on securing key towns, training Afghan forces and bolstering local government.

But the need to cut off the insurgency's supply routes to sanctuaries in neighboring Pakistan has led to a renewed emphasis on more conventional "targeting" operations, said General James Cartwright, vice chair of the Joint Chiefs of Staff.

"When we started, we probably were more aligned with counterinsurgency (strategy). The emphasis is shifting," Cartwright said last week.

"We need to reduce those lines of communication and reduce that flow to the best of our abilities," Cartwright said at an event at the National Press Club.

The balance of the US force was "starting to shift to have an element of counter-terrorism larger than we thought we were going to need when we started," he said.

The expansion of counter-terrorism raids also appears to fit in with the need to drive the Taliban to the negotiating table, as US military leaders have long stated that the insurgents must sense they are losing ground on the battlefield before they engage in genuine peace talks.

The previous commander in Afghanistan, General Stanley McChrystal, scaled back air strikes and artillery to try to reduce civilian casualties, but his successor, General David Petraeus, has taken a more aggressive approach.

US aircraft flew 850 combat sorties in November, three times the number for the same month last year, according to the US Air Force.

From January to the end of November, warplanes carried out 30,000 close air support missions for troops on the ground, a 13 percent increase compared with the whole of 2009, it said.

In the past six months, coalition forces have carried out more than 7,000 special operations missions, killing or capturing more than 600 militant leaders and inflicting heavy losses on insurgent fighters, with 2,000 rank and file soldiers killed, the NATO-led force told The Long War Journal.

More firepower will be on display soon in southern Afghanistan, where Marines will have M1A1 tanks in their arsenal -- the first use of American tanks in the war.

The intensifying pace of lethal operations has been accompanied by record casualties among US and NATO-led forces, in the most deadly year yet in the nine-year-old war with 693 soldiers killed, according to the independent website

Pentagon officials say the increase in manhunts is a natural result of the troop buildup, and Defense Secretary Robert Gates said the approach in the war remained "a mix" of both nation-building and counter-terrorism.

He described the effort in eastern Afghanistan as a "disruption activity" with US troops trying to stop insurgents from coming across the Pakistani border.

In the south, US-led troops were pushing the Taliban out of towns and then holding the populated areas, he said.

"You need to understand the strategy in one part of the country will be different in another part," Gates told reporters last week on his way back to Washington.

A crucial part of the US strategy includes an expanded covert bombing campaign against Al-Qaeda and insurgent leaders in the northwest tribal belt in Pakistan.

The CIA strikes have been steadily growing, with 108 attacks by drones in 2010, compared to 53 last year, mainly in North Waziristan, where the Pakistan army has so far failed to extend an offensive against militants there, according to the New America Foundation.

The drone raids have killed 809 militants this year, compared to 405 the year before.