Helmand has been the front-line in battles between the Taliban and international forces in recent months, and has seen some of the bloodiest fighting in the past two years.
It is also the largest opium-producing area in the world.
More than 4,300 people have died in insurgency-related violence this year, according to an Associated Press tally of figures from Western and Afghan officials.
The AFP news agency also reported on Sunday that unidentified men kidnapped a Bangladeshi development worker just south of Kabul, the Afghan capital - the latest in a string of abductions.
It was not clear who abducted the man, an employee of the Bangladesh Rural Advancement Committee (BRAC), on Saturday near the town of Pul-i-Alam.
"Six persons entered the office and forcefully took him away," AFP reported Gunendu Roy, the head of BRAC's mission in Afghanistan as saying.
The man, who was not identified, had been working on a microfinance project intended to help the poor.
Meanwhile, in central Ghor province, drug smugglers hauling an estimated 1,000 kilogrammes of opium clashed with police in Shahrak district, leaving one officer dead, said Shah Jahan Noori, a provincial police chief.
Three smugglers were arrested, he said.