The United States is planning to take control of all military operations in Afghanistan next year with an Iraq-style troop surge after becoming frustrated at Nato’s failure to defeat the Taliban.

Plans are being drawn up to send as many as 15,000 extra troops to Afghanistan with a single US general always in command, as in Iraq, defence sources said.

The Pentagon is also pushing for a permanent “unified command” in the south of the country that would sideline the Dutch and the Canadians.

At present, control of the south is rotated between the British, Dutch and Canadians, the three countries that provide the bulk of the troops.

From October next year, when the UK will take over from the Dutch, command of the south is expected to alternate between the British and the Americans.

Although final decisions cannot be made until the new US administration takes over in January, plans are being drawn up to send two to three US combat brigades – a total of between 8,000 and 12,000 men, the sources said.

Lawrence Korb, a defence expert at the Centre for American Progress, a Democratic think tank in Washington, said: “There is no doubt that the US wants to change the command structure as things have deteriorated in Afghanistan.”

Both Barack Obama, the Democrat presidential candidate, and John McCain, his Republican opponent, have spoken of using “two to three [combat] brigades for the surge, amounting to 8,000-12,000 troops”, Korb said. “There will be a US general and the forces will be under US command.”

The surge will also see US and other coalition special forces, which operate separately from the Nato command, absorbed into a single US command for the whole of Afghanistan.

A report written by Barry McCaffrey, a retired US general, that is highly critical of the command structure in Afghanistan is circulating at senior levels within the Pentagon. “There is no unity of command in Afghanistan,” it says.

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