The suicide attack occurred as the army patrol was crossing a bridge in Gereshk, a town just north of the provincial capital of Lashkar Gah. Provincial spokesman Dawood Ahmadi said all the victims were civilians, most of them vendors selling goods along the highway.

Helmand province has been the scene of some of the heaviest fighting in recent weeks, including last month's operation by US, Nato and Afghan forces to take control of the Taliban-controlled town of Marjah which is south of Lashkar Gah.

Taliban forces in Marjah scattered in the face of the massive allied assault but are fighting back with ambushes and hidden bombs. Local residents have said the Taliban remain strong throughout the province despite the allied takeover of Marjah.

The attack against the New Year's celebrants took place in Khost province, another flash point area along the border with Pakistan.

Khost police Chief Yaqoub Khan was about 40 yards away from the blast but was not injured. He said Afghan and US forces provided enough security to prevent a deadlier attack "but unfortunately the enemy uses every means and planted a bomb just off the road".

Late Saturday, two other explosions shook the city of Jalalabad in Nangarhar province north of Khost, causing no damage or casualties.

The Nangarhar police spokesman, Ghafour Khan, said the bombs went off in a thinly populated area and were designed "to create fear among the people" who were attending concerts and public events marking the Afghan New Year, or Nowruz, which is also celebrated in Iran and elsewhere in central Asia.

Separately, two other civilians died and four were wounded when a roadside bomb went off near a crowd of people celebrating the Afghan New Year at a mountaintop shrine in eastern Afghanistan, a police commander said.