Marjah, Afghanistan: US and Afghan forces traded gunfire with insurgents shooting from haystacks in poppy fields in the Taliban stronghold of Marjah as they pressed ahead in Nato's assault on the militants' heartland in southern Afghanistan.

Hoping to avoid prolonged gunbattles, Marines called for long-range artillery support to disperse sniper squads harassing their advance into the town. For the first time since the offensive began on Saturday, US forces fired the non-lethal artillery "smoke shells" in a bid to intimidate enemy fighters who also lobbed back rockets and mortars at them.

"We are trying not to be decisively engaged so we can progress, but we're having some difficulty right now," said Lima Company commander Capt. Joshua Winfrey.

Despite the continued firefights, Marine officials said the resistance was more disorganised than in previous days.

"We're not seeing coordinated attacks like we did originally. We're still getting small-arms fire but it's sporadic, and hit-and-run tactics," said spokesman Capt. Abraham Sipe. "As a whole, while there is still resistance, it is of a disorganised nature."

Three civilians killed

Three more Afghan civilians were killed in the assault, Nato forces said, highlighting the toll on the population from an offensive aimed at making them safer.

The deaths — in three separate incidents — come after two errant US missiles struck a house on the outskirts of Marjah on Sunday, killing 12 people, half of them children. Afghan officials said three Taliban fighters were in the house at the time of the attack.

About 15,000 Nato and Afghan troops are taking part in the massive offensive around Marjah — the lynchpin of the Taliban logistical and opium poppy smuggling network in the militant-influenced south.

As the assault in Marjah — the lynchpin of the Taliban logistical and opium poppy smuggling network in the militant-influenced south — continued, the extremist group received a blow with the news that its top military commander had been arrested in Pakistan.

Mullah Abdul Gani Baradar, the group's No. 2 leader behind Afghan Taliban founder Mullah Mohammad Omar and a close associate of Osama Bin Laden, was captured in the port city of Karachi, US and Pakistani officials said, speaking on condition of anonymity because of the sensitivity of the information. The arrest appeared to have occurred as many as ten days ago, and it was unclear if it had any effect on the Marjah battle.

The offensive is the biggest joint operation since the 2001 US-led invasion of Afghanistan, and a major test of a retooled Nato strategy to focus on protecting civilians, rather than killing insurgents.

But in two incidents confirmed yesterday, Afghan men came toward Nato forces and ignored shouts and hand signals to stop, Nato said. Troops opened fire and killed them.

In the third incident, two Afghan men were caught in the crossfire between insurgents and Nato forces. Both were wounded and one died of his injuries despite being given medical care, Nato said.

Nato officials have reported only two coalition deaths so far - one American and one Briton killed Saturday.