The U.S. 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. NATO has already reported more than 200 Taliban killed in the operation.

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 in Tuesday's fighting 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.

A Panjwayi district council member, Haji Agha Lalai, said bombings by NATO warplanes have killed 21 civilians over the past three days in an area called Zungawad. NATO spokesman Maj. Scott Lundy said he had no immediate details to support Lalai's claims.

The bloody contest between resurgent Taliban militants and U.S. and NATO forces has left hundreds dead in each of the past four months - the deadliest spate of violence since the pro-al-Qaida Taliban regime's 2001 ouster.

The latest clashes came as NATO's leaders and diplomats were in Afghanistan to sign a security and development accord with President Hamid Karzai and to assess progress in the alliance's mission to tame the volatile south.

"The fight must be won and will be won," NATO Secretary General Jaap de Hoop Scheffer told reporters. "We should win because not winning means Afghanistan becoming a failed state again."

De Hoop Scheffer acknowledged that NATO forces had met stiffer resistance than expected since they took command of the south from a U.S.-led coalition a month ago.

"The spoilers are testing out NATO to see if NATO is as robust as the coalition. The answer as we now see is, 'Yes.'"

The Afghan Defense Ministry on Tuesday said 200 militants have 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. No further details were available.

Five Canadian soldiers have also been killed, one in "friendly fire" by a U.S. warplane Monday.

Mullah Dadullah, the Taliban military commander for south and southeastern Afghanistan, on Monday rejected NATO's claim of over 200 dead.

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

Lundy, the NATO spokesman, said earlier Tuesday that an estimated 700 militants were "trapped" in an area spanning several hundred square kilometers (miles) in Panjwayi and Zhari districts, some in fortified compounds, others moving in the open. NATO has also reported that 80 Taliban have been arrested and a further 180 have fled the fighting.

"It's a complex battle space. Some (Taliban) elements are fixed, others are moving," Lundy said.

The alliance has so far not confirmed any civilian casualties during Operation Medusa in Panjwayi, saying residents had evacuated before it began Saturday, as NATO had dropped leaflets and made public announcements in the preceding days advising them to leave the area.

But a hospital in Kandahar on Tuesday reported that a boy and girl had been killed and at least nine other civilians have been treated for injuries from the fighting since Sunday.

Copyright 2006 Associated Press. All rights reserved.