The Taliban have launched a major attack on a construction company building a road from Lashkar Gah to Sangin in southern Afghanistan, according to reports.
As many as 30 people were killed during the day-long attack in Helmand province on Thursday, officials say.
The exact number and identity of casualties is not yet clear.
But bodies have begun arriving at a hospital in the provincial capital of Lashkar Gar, the officials said.
The nationalities of the dead have not been released, but it is believed that both the security company and the construction company employed Afghan nationals.
The head of the security company guarding the construction team told the BBC a large number of Taliban advanced on them from the direction of Kandahar.
Mohammad Qoadas, of the Durai Sangeen security firm, said 22 guards had been killed and 16 were injured in the attack.
"There were hundreds of Taliban who attacked us," he said.
He said the attack began in the early hours of the morning and lasted 15 hours.
"International forces arrived to assist us, but by then we had defeated them," Mr Qoadas said.