The US is escalating its assault on the Taliban with a sharp rise in bombing and missile raids, more relaxed rules on the destruction of civilian property and the deployment of heavily armoured M1 Abrams tanks to Afghanistan for the first time.

But aid groups warned today that the dramatic increase in air strikes in recent months is contributing to "rapidly deteriorating" security for most Afghans and what is expected to be a rising number of civilian casualties.

The shift away from the previous emphasis on protecting civilians from the insurgents has drawn stinging criticism from the Afghan president, Hamad Karzai, but American military commanders say that it is working.

The number of "special operations" missions targeted at Taliban leaders has more than tripled since General David Petraeus took over as Nato commander in Afghanistan in July. Nato planes dropped about 1,000 bombs and missiles last month, more than at any time since the early stages of the war in 2001.

One US official told the Washington Post that the new strategy is forcing back the Taliban.

"We've taken the gloves off, and it has had huge impact," the official said.

The military's claim of new successes with aggressive tactics appears in part aimed at strengthening Petraeus's hand at the Nato meeting in Lisbon. It will also be used by the general to argue that his military strategy is producing results when the White House reviews the conduct of the war next month.

The Americans say they plan to deploy a company of M1 Abrams tanks, considered among the most lethal of US military vehicles with an ability to destroy buildings more than a mile away. The fast 68-tonne tanks will be used by US marines in Helmand province where the Americans say the Taliban are equipped with weapons such as rocket propelled grenades.

Under Petraeus's predecessor, General Stanley McChrystal, who was sacked by the White House over criticism of his civilian superiors, the US counter-insurgency strategy laid a heavy emphasis on separating and protecting Afghan civilians from the Taliban.

Although that is not being formally abandoned, Petraeus has decided to take the fight to the insurgents and American forces have taken a more aggressive stance.

McChrystal's emphasis on protecting civilian lives did not sit well with many in the military, including front line troops who were prevented, for example, from destroying houses that might be used to hide roadside bombs or provide shelter for attack. American troops now routinely destroy houses they believe to be a threat. But the shift has angered Karzai who has argued that night raids by special forces and other tactics are fuelling support for the Taliban.

A report by Oxfam and about 30 other foreign and Afghan aid agencies today said that the more aggressive tactics, particularly the air strikes, threaten to reverse a reduction in civilian deaths caused by foreign forces.

Restraints on the use of air power by Nato led to a 30% drop in deaths and injuries caused by foreign forces in the first six months of this year against the same period in 2009. However, those restraints have now been eased.

"Security for the vast majority of Afghans is rapidly deteriorating. It is likely that increased violence in 2011 will lead to more civilian casualties," the report said.