Ten of thousands of Afghan civilians are abandoning an area of central Helmland where UK and US forces are set to launch one of the biggest operations of the year.

The evacuation of most civilians from the town of Marjah and surrounding areas will give commanders greater leeway to use mortars-and-air-to ground missiles which have enraged Afghans in the past when responsible for civilian deaths.

US generals have unusually made no secret of their plan for a major onslaught against the town close to Helmand's besieged provincial capital, Lashkar Gah.

Larry Nicholson, commander of the 2nd Marine Expeditionary Force which will spearhead the fight, has said he is "not looking for a fair fight".

Marjah is regarded as a stronghold of both Taliban insurgents and drug trafficking networks which must be removed to "protect" the people who live there. But so far the warnings have only had the effect of encouraging civilians to flee.

Abdul Salam, who has an extended family of 14 in the Marjah area, said his village looked almost deserted as most of its families had left for the cities of Lashkar Gah, Kandahar and Herat.

"They just picked up their jewellery and other small valuables and left everything behind," he said.

However, some civilians had remained because they could not afford to leave.

"People know they cannot protect everything, and they are more concerned about saving their lives than their houses. The people cannot protect their country from the infidels, so how can we protect our houses?"

The counterinsurgency plan pushed by Stanley McChrystal, the US commander of all Nato forces in Afghanistan, aims not to alienate the population. But a Marjah resident, an elder reached by phone, who was not prepared to give his name, said he had evacuated his family a week ago because he feared "the worst attack ever".

"Always when they storm a village the foreign troops never care about civilian casualties at all. And at the end of the day they report the deaths of women and children as the deaths of Taliban," he said.

A spokesman for the International Security Assistance Force, as the Nato troops are known, said that the main reason for publicity for the operation was to encourage insurgents to leave, but if civilians were also encouraged to evacuate that would be "helpful".

Most of the extra 30,000 US troops earmarked for the Afghan campaign will support Nato efforts in areas where the alliance has a presence, in a bid to keep insurgents out of villages. The battle for Marjah will therefore be a relatively rare push into an area not yet cleared of insurgents.

It is regarded as particularly important because an estimated 100,000 people live in the area – a relatively dense population for a largely desert province dotted with rural communities.

Marjah is also on the south-western doorstep of Lashkar Gah, home to the headquarters of the British military and civilian efforts in the province.

The fraught security in Lashkar Gah was highlighted yesterday when a motorbike packed with explosives detonated close to a crowd gathered on the city outskirts to watch a dog fight; it killed at least three people and injured at least 26, including seven children.