Kabul - The Taliban is at its strongest since it was ousted from power in 2001 as Afghanistan prepares to vote this week in a presidential election, the commander of NATO and US forces in Afghanistan said Tuesday.

"The insurgency has grown," US General Stanley McChrystal said in an interview with German media at NATO headquarters in Kabul. "It has grown geographically, and it has grown in levels of violence."

"We have a very real challenge to the sovereignty and the people of Afghanistan," said the four-star general who took up his Afghanistan command in June after serving as commander of US special operations and being credited with leading a successful counterinsurgency programme in Iraq.

He added, however, that the capabilities of the Afghan government had also grown since 2001 and the numbers of the Afghan army and police risen substantially in the past two years.

"I do not think we will lose this contest to the insurgency," he said. "I believe we'll win." (dpa)