US troops in Afghanistan's Helmand province, 2 Jul 2009

U.S. Marines have suffered their first casualties of a new major offensive in Taliban-controlled parts of southern Afghanistan.

The U.S. military says one Marine was killed and several others wounded as they were taking up positions in Taliban strongholds in Helmand province.

Thousands of U.S. Marines and hundreds of Afghan soldiers and police are taking part in the operation, which began with a pre-dawn air and ground assault Thursday.

Military officials said troops only encountered sporadic resistance from militants, and were continuing "clearing operations" in the Helmand River valley region.

The offensive marks the first major operation under U.S. President Barack Obama's revamped strategy to defeat an increasingly violent Taliban insurgency.

Thursday's operation caused concern in neighboring Pakistan. The Pakistani military said it had re-deployed some of its troops to stop insurgents fleeing the Helmand offensive.

U.S. commanders say Operation Khanjar, Strike of the Sword, differs from previous efforts because of its size and its goal of holding on to captured Taliban territory.

A spokesman for the U.S.-led coalition, Sergeant Charles Marsh, said the combined U.S. and Afghan offensive is designed to provide security for population centers.

He said it also aims to connect locals with their legitimate government, while establishing stable and secure conditions for upcoming national elections as well as enhancing security for the future.

In a White House interview Thursday, Mr. Obama said the U.S. and its allies need to help Afghanistan build up its security forces and help Pakistan protect its borders against terrorists.

In other violence, Afghan Interior Ministry said security forces killed nine militants in eastern Zabul province and discovered a large cache of explosives.