by Patrick Baz
MARJAH, Afghanistan (AFP) – US-led troops waging a huge offensive against the Taliban in southern Afghanistan risked becoming bogged down Tuesday, running into pockets of resistance and scores of planted bombs.

The assault on the militant stronghold of Marjah is the first major test of US President Barack Obama's strategy to crush an eight-year insurgency and one of the biggest since the 2001 US-led invasion brought down the Taliban regime.

US and Afghan military officials said remote-controlled bombs were hampering the progress of the assault on Marjah in the Nad Ali district of the southern province of Helmand, controlled for years by militants and drug lords.

The bombs, the main weapon in the Taliban arsenal and the principal killer of foreign troops in Afghanistan, are being discovered in their hundreds, said the Afghan army's chief of staff.

"Hundreds of mines have been discovered in different areas," Besmillah Khan told reporters, referring to improvised explosive devises, or IEDs.

"We are advancing slowly because areas have been mined," he said on the fourth day of the offensive in one of the world's largest opium-producing areas.

US Marines are leading 15,000 troops in the assault dubbed Operation Mushtarak ("Together" in Dari), to drive out militants and allow the Afghan government to re-establish control.

Of the 75 foreign troops killed in Afghanistan so far this year, most have been from IEDs, which US intelligence officials say are responsible for up to 90 percent of foreign troop deaths.

A spokesman for the US Marines, which are leading the operation, said troops have been surprised by the number of IEDs found during their advance.

"We are definitely finding more than we expected," said Lieutenant Josh Diddams, of Taskforce Leatherneck, adding: "It's a slow process."

He said progress was being slowed "in some pockets" as Taliban fighters stood their ground and fought, or used guerilla-style hit-and-run tactics, firing on combined troops from residential compounds or mosques.

Rules of engagement prevent the forces returning fire on homes or mosques.

Brigadier General Larry Nicholson, who commands the Marines in southern Afghanistan, expected the operation to last for 30 days, Diddams said.

On Monday, a senior Afghan commander had said that the coalition forces controlled almost all of Marjah and Nad Ali and that the Taliban had left the area.

The Red Cross said IEDs planted on roads were also preventing casualties from to hospital in the provincial capital Lashkar Gah, 20 kilometres (12 miles) away from Marjah.

"We have had an increase in people coming in in the past 72 hours, we have walking wounded and the problem is to get those who need more help to where they can get it," said Bijan Farnoudi, the ICRC's communication coordinator.

Most casualties coming to the ICRC first aid post in Marjah were men, he said, adding: "It is possible that a good proportion of them are fighters."

Their injuries were consistent with battlefield wounds, he said.

Limiting civilian casualties is key to winning hearts and minds in the operation against a Taliban force estimated at up to 1,000 fighters, and as many as 400 families fled the area in the buildup to the offensive.

NATO acknowledged responsibility for the deaths on Sunday of 12 Afghans when two rockets missed their target and landed on a compound as troops came under fire in Nad Ali.

On Monday, NATO said five civilians were accidentally killed in an air strike in the neighbouring province of Kandahar.

Two NATO soldiers have been killed in Mushtarak, while another six British and American soldiers have died elsewhere in southern Afghanistan since the assault was launched on Saturday.

An AFP photographer on the outskirts of Marjah said troops had advanced slowly, coming under Taliban fire and hunting for IEDs, as they sought to reassure residents that they were in the area to stay.

Obama has ordered more than 50,000 extra US troops to Afghanistan since taking office in January 2009, with the final reinforcements due to bring to 150,000 the total number of US and NATO-led troops in the country by August.

Western commanders say Mushtarak is a show of force designed to implement counter-insurgency tactics drawn up by the top commander US General Stanley McChrystal to push out militants and pave the way for Afghan sovereignty.