Reuters said there was no immediate explanation for the attack late on Thursday in the Sangin district of Helmand province in which the roadcrew workers and security guards were killed, although construction crews are frequently targeted.

“A group of Taliban attacked the site with machine guns and rockets, killing 25 of my workers,” said an official from the Afghan Construction company who identified himself as Aqa January

Mohammad Mamaluddin, the Helmand deputy police chief, said later the death toll had risen to 30 and that another 17 were wounded.

He said the attackers had also set fire to machinery and taken about 12 four-wheel drive vehicles.

Dawood Ahmadi, a spokesman for the Helmand governor, said 12 bodies had been taken to a hospital in the provincial capital Lashkar Gah, along with some of the wounded.