Squads of Marines and Afghan soldiers slowly pressed deeper into the Taliban stronghold of Marjah today, painstakingly clearing out booby-trapped houses one by one.

Homemade bombs and mines slowed the advance of thousands of U.S., British and Afghan soldiers in NATO's most ambitious effort yet to break the militants' grip over their southern heartland.

Using metal detectors and sniffer dogs, U.S. forces found caches of explosives rigged to blow as they went from compound to compound. They also discovered several sniper positions, freshly abandoned and booby-trapped with grenades.

NATO said yesterday it hoped to secure the area in days, set up a local government and rush in development aid in a first test of the new U.S. strategy for turning the tide of the eight-year war. The offensive is the largest since the 2001 U.S.-led invasion of Afghanistan.

Most of the Taliban appeared to have scattered in the face of overwhelming force, possibly waiting to regroup and stage attacks later to foil the alliance's plan to stabilize the area and expand Afghan government control in the volatile south.

NATO said two of its soldiers were killed in the first day of the operation—one American and one Briton, according to military officials in their countries. Afghan authorities said at least 27 insurgents were killed.

More than 30 transport helicopters ferried troops into the heart of Marjah before dawn yesterday, while British, Afghan and U.S. troops fanned out across the Nad Ali district to the north of the mud-brick town, long a stronghold of the Taliban.

Maj. Gen. Gordon Messenger told reporters in London that British forces “;have successfully secured the area militarily”; with only sporadic resistance from Taliban forces. A Taliban spokesman insisted their forces still controlled the town.

President Barack Obama was keeping a close watch on combat operations, White House spokesman Tommy Vietor said.

The president got an update from his national security adviser, Gen. Jim Jones, later yesterday. Vietor said Defense Secretary Robert Gates also will have the top U.S. commander in Afghanistan, Gen. Stanley McChrystal, brief Obama today.

In Marjah, Marines and Afghan troops faced little armed resistance. But their advance through the town was impeded by countless land mines, homemade bombs and booby traps littering the area.

Throughout the day, Marine ordnance teams blew up bombs where they were found, setting off huge explosions that reverberated through the dusty streets.

The bridge over the canal into Marjah from the north was rigged with so many explosives that Marines erected temporary bridges to cross into the town.

“;It's just got to be a very slow and deliberate process,”; said Capt. Joshua Winfrey of Stillwater, Okla., a Marine company commander.

Lt. Col. Brian Christmas, commander of the 3rd Battalion, 6th Marines, said U.S. troops fought gunbattles in at least four areas of the town and faced “;some intense fighting.”;

To the east, the battalion's Kilo Company was inserted into the town by helicopter without meeting resistance but was then “;significantly engaged”; as the Marines fanned out from the landing zone, Christmas said.

Marine commanders had said they expected between 400 and 1,000 insurgents to be holed up in Marjah, a town of 80,000 people that is the linchpin of the militants' logistical and opium-smuggling network in the south.

The offensive, code-named “;Moshtarak,”; or “;Together,”; was described as the biggest joint operation of the Afghan war, with 15,000 troops involved, including some 7,500 in Marjah itself. The Kaneohe-based 1st Battalion, 3rd Marine Regiment, is part of the offensive.