Image caption Gen David Petraeus took battlefield command in Afghanistan last summer

The US commander in Afghanistan has said the Taliban's momentum has been halted in key areas, keeping the US on course to start withdrawing in July.

Gen David Petraeus, commander of US forces in Afghanistan, was giving his first formal assessment to Congress since taking over the role last June.

He said progress so far meant officials could recommend shifting some control to the Afghan forces in the spring.

US forces in Afghanistan number 97,000, alongside 45,000 from Nato allies.

Gen Petraeus took over command of US forces in Afghanistan after Gen Stanley McChrystal was asked to step down in June 2010.

Testifying before the Senate Armed Services Committee, Gen Petraeus said that the Taliban's momentum "has been arrested in much of the country and reversed in a number of important areas".

He said he was optimistic about the course of the fight going forward, after the coalition's recent military successes.

"We believe that we will be able to build on the momentum achieved in 2010, though that clearly will entail additional tough fighting," he said.

Analysis Gen David Petraeus is reprising his role as saviour of troubled expeditionary wars. His message to the Senate Armed Services Committee: events in Afghanistan are slowly turning in favour of the US, its allies, and the Kabul government. Plans to begin the handover to the Afghan security forces this summer, and to complete it by the end of 2014, are on track. As always his demeanour was calm, his attention to detail remarkable. And yet nearly two-thirds of Americans - according to the latest ABC News-Washington Post poll - see the war as "not worth fighting". In the face of such pronounced public scepticism, the American military establishment still sees the stakes as very high. Next to Gen Petraeus sat Michele Flournoy, Under Secretary of Defense. US success in Afghanistan, she said, would be a "calculus-changing event" among actors in the region who "have been hedging". In other words - if the US can succeed in Afghanistan, it will change the regional security equation throughout South Asia in its favour.

However, he warned that the successes so far were "fragile and reversible" and that adequate funding was necessary to avoid jeopardising military gains to date.

"I am concerned that levels of funding for our State Department and USAID partners will not sufficiently enable them to build on the hard-fought security achievements of our men and women in uniform," he said.

In his opening statement, Senator John McCain, the top Republican on the Armed Services panel, suggested that "strategic patience" should be cultivated.

"This patience will be all the more essential as we wrestle with two other key challenges," he said.

"The first is governance and corruption. American taxpayers want to know that the vast resources they are committing to this war effort are not being wasted, stolen, or misused by Afghan officials.

"A second key challenge stems from Pakistan."

Members of Congress are due to roll out a resolution calling for Mr Obama to withdraw US forces from Afghanistan either in 30 days or no later than the end of 2011.

The measure represents impatience with the war and increasing budget pressures, but it has failed in the past and is likely to fail again.

Gen Petraeus made his comments as a new ABC News-Washington Post poll showed a record low in support for the war in Afghanistan among American.

Only 31% of those surveyed said the decade-old war had been worth fighting, with 64% saying it was not worth fighting.

The poll also suggests 73% of Americans believe the US should withdraw a substantial number of its combat forces from Afghanistan this summer, but only 39% think it will.

Last week US defence secretary Robert Gates, on an unannounced visit to Afghanistan, said the US was "well-positioned" to begin withdrawing troops from Afghanistan in July.

He also apologised over the deaths of nine Afghan boys the weekend before in a Nato air strike.

President Barack Obama has said that civilian deaths are the main cause of a worsening in the relationship between Afghanistan and the US.