MARJAH, Afghanistan — Explosions rumble through this former Taliban stronghold three or four times a day — an ominous sign that the insurgents have not given up despite losing control of this town to U.S. and Afghan forces about two weeks ago.

Last week, Army Lt. Gen. Michael L. Oates, the U.S. general in charge of a Pentagon program to combat roadside bombs, told a congressional committee that the number of homemade explosives in Afghanistan had nearly doubled in the past year and "the number of casualties has reflected that."

The disturbing trend is starkly clear here in Marjah, which had been the biggest community under Taliban control in the south until a major military operation was launched last month to push out the insurgents.

Taliban fighters scattered but have not abandoned the fight — and are using homemade bombs as their weapon of choice.

New bombs are planted every night, even though Marines say they find and render safe more of them than explode. The bombs are often placed in spots where the Marines stopped on patrol the day before, or into holes from previous explosions so the upturned earth doesn't look suspicious.

Since U.S. and Afghan forces seized control of Marjah, they have been working to build up trust in the community. They hope the strategy will pay off with more and more tips about where the Taliban have planted bombs, which the military calls improvised explosive devices or IEDs.

But the process is slow. Lt. Col. Calvert Worth, commander of the 1st Battalion, 6th Marine Regiment, said his troops found or hit more than 120 homemade bombs in their first 30 days here.

Coping with daily blasts and hunting for bombs takes up time that could be spent helping set up a local Afghan administration, which NATO considers key to keeping Marjah from returning to insurgent control.

Whenever the Marines meet with Marjah residents, they make the point that the Taliban bombs pose a threat to Afghan civilians in the town, too.

"It's not really stopping us because we're still going out and talking with the people," said Capt. Carl Havens, commander of Alpha Company, which has had three vehicles hit by bombs in the past week.

"We talk about how the Taliban don't care about you or us," he said.

As the Marines improve their bomb-detection skills, the insurgents have begun to adapt to Marine tactics.

Units have found decoy bombs planted in the middle of the road. That forces Marines out of their vehicles to make sure the bombs are fake. Real bombs are planted along the roadsides in hopes that some of the Marines may step on them, according to Capt. Michael Woodie, intelligence officer for Alpha Company.

"There's a lot of eyes and ears watching," Woodie said. "On patrols, there's guys 'turkey-peeking' on top of roofs. Sometimes you see a guy pointing and counting. They're watching what we do when we find IEDs."

On Thursday, two Mine-Resistant Ambush-Protected vehicles — heavily armored personnel carriers known as MRAPS — struck bombs within a couple of hours. No one was seriously wounded because the hulls are so strong.

With the Americans using more heavily armored vehicles, Taliban fighters are increasingly planting smaller bombs, aimed at foot patrols.