Nato already has reported more than 200 Taliban killed in the operation.

The US troops, operating under Nato command, clashed with the militants in Panjwayi district of Kandahar province, where an offensive began over the weekend to flush out hundreds of Taliban fighters.

Maj. Quentin Innis, a Nato spokesman, said the troops had identified Taliban positions and the two sides had exchanged fire. He said the estimate of 50 to 60 killed was based on reports from troops looking through "weapons sights and other observation devices."

He said there had been no Nato or Afghan troop casualties.

It wasn't possible for reporters to reach the site of the battle to independently confirm the death toll.

The Afghan Defence Ministry also said 200 militants had died since Saturday increasing its previously reported toll of 89. The dead included four Taliban commanders and 12 of their bodyguards, a ministry statement said, citing intelligence reports.

Five Canadian soldiers have also been killed, one in a friendly fire incident Monday involving a US warplane.

Mullah Dadullah, the Taliban military commander for south and southeastern Afghanistan, has rejected Nato's claims of more than 200 dead.

Qari Yousaf Ahmadi, who claims to speak for the Taliban, said if Nato had killed so many Taliban fighters, they should show them to the media. He also denied that hundreds of Taliban militants were trapped in Panjwayi, and said its fighters were battling Nato and Afghan forces there. He spoke to an Associated Press reporter by phone from an undisclosed location.