US Marines and Afghan soldiers continue to meet pockets of resistance
US forces have faced sporadic resistance around the Taliban haven of Marjah as a major offensive in southern Afghanistan completes its fourth day.
The progress of US troops has been hampered by sniper fire and improvised explosive devices (IEDs) in some areas.
British and Afghan troops are reported to be advancing more swiftly in the nearby district of Nad Ali.
A Nato spokesman said they had begun setting up joint patrol bases to provide a permanent security presence.
Unrelated to the Marjah offensive, an air strike in neighbouring Kandahar province killed five civilians who were mistakenly believed to have been planting roadside bombs.
The deaths come after two US missiles struck a house on the outskirts of Marjah on Sunday, killing 12 people, half of them children.
Nato has stressed that the safety of civilians in the areas targeted is its highest priority.
Lt Gen Nick Parker, the most senior British officer in Afghanistan, told the BBC it was absolutely unacceptable to have civilian casualties, whatever the circumstances, and that announcing the offensive well in advance had helped save lives.
Dawud Ahmadi - a spokesman for Helmand Governor Gulab Mangal - told the BBC's Pashto service that Afghan National Army and Nato forces are clearing areas around Marjah of mines.
"There is still sporadic Taliban firing from residential areas in the north of the town, but we are not using air power or heavy bombardments to dislodge them because we want to avoid civilian casualties," he said.
Mr Ahmadi said that 1,240 familes had been displaced and evacuated from Marjah - and all had received aid in the provincial capital, Lashkar Gah.
He said the aim of the operation was to rid Marjah of militancy and drugs traffickers and then hand it over to Afghan police before establishing a civil administration for the area.
Earlier, Afghan Gen Ghulam Mahaiuddin told Reuters news agency that many Taliban militants had "escaped" and that his forces were now searching houses for weapons and ammunition.
They were encouraging those villagers who had left the area before the military operation to return, he said.
But despite Afghan government claims that the insurgents were on the run, small teams of insurgents repeatedly attacked troops and mine-clearing vehicles with rocket, rifle and rocket-propelled grenade fire.
US Marines have twice unsuccessfully tried to clear a bazaar area in Marjah of enemy positions.
Lt Josh Diddams told AFP that in some pockets in Marjah, Taliban militants were standing their ground and fighting, or were firing on US and Afghan forces from homes and mosques.
Marjah resident Haji Mohammed Jan told the BBC the Taliban had tried to stop people leaving, but he and others had managed to escape.
Operation Moshtarak, meaning "together" in the Dari language, is the biggest coalition attack since the Taliban fell in 2001.
The operation is also considered the first big test of US President Barack Obama's new "surge" strategy for Afghanistan.
Allied officials have reported only two coalition deaths so far - one American and one Briton killed on Saturday.
Two other Nato soldiers died on Monday in unrelated bomb strikes in Helmand, military spokesman Sgt Kevin Bell said.
Afghan officials said at least 27 insurgents had been killed so far in the offensive.