It was not immediately possible to verify the authenticity of the Pashto-language statement. It was e-mailed to The Associated Press by Abdul Hai Mutmahin, who used to be a spokesman for the fundamentalist regime before it was ousted by US-led forces in late 2001.

“I call upon the Muslim nation to be united against the clever occupation force until the aggressors leave our soil,” the statement said. “Fighting jihad is an obligation. Abandoning jihad is a big sin and a cause for humiliation of Muslims. Stand with us with your resources, with your lives.”

Purported Taleban spokesmen occasionally release statements they claim are by Omar, who is believed hiding in rugged mountains along the Afghan-Pakistan frontier. Wednesday’s statement was the second received by e-mail.

Omar warned in the statement that the rebels will “intensify their attacks against the occupiers.”

A US military spokesman said he was not aware of the statement, but would investigate it.

A Defence Ministry spokesman, Gen. Mohammed Zahir Azimi, dismissed it as propaganda.

“The enemies of the country have done everything they are capable of doing. There’s nothing more they can do,” he said. “The Afghan army is prepared to counter any violence.”

In the latest fighting, suspected Taleban rebels ambushed police late Tuesday as they were driving in mountains in Helmand province’s Dishu district, said Ghulam Muhiddin, the provincial administrator.

Another purported Taleban spokesman, Qari Mohammed Yousaf, said insurgents beheaded the men after the battle, but this could not be confirmed.