KABUL, Afghanistan — Fierce bouts of factional fighting erupted on Friday across Afghanistan, and a Turkish road engineer was reported kidnapped by suspected Taliban fighters, officials said Saturday.

Fighting between the local police and a militia chief broke out on Friday in the center of the town of Gereshk, in southern Afghanistan, killing at least six people just yards from a U.S. Special Forces base, local officials said.

Factional fighting was also reported in northern Afghanistan, where rival warlords have been vying for months for control of territory. Five soldiers were killed in clashes between two groups on Friday in Sar-e-Pul province, an official from one faction told Reuters.

The violence was another blow to the government of President Hamid Karzai. But the biggest setback was the kidnapping of the engineer, who was working on the American-financed project to improve the main highway south from Kabul. It is the biggest construction project in the country and a flagship of American commitment to reconstruction.

The engineer and his Afghan driver were reported kidnapped on Thursday, near the town of Shajoy, the governor of Ghazni province, Hajji Asadullah Khalid, said in a telephone interview on Saturday. A spokesman for American officials confirmed the account.

The driver was released Friday with a note demanding the release of Taliban prisoners, the governor said. He reported that the note said, ‘‘We have your engineer, and you have our six Taliban in your prisons.''

Factional violence and the lack of security for reconstruction and aid workers are emerging as a serious problem for the government. The 11,500 members of the American-led coalition are trying to find fighters for al-Qaida and the Taliban and to create the conditions needed for stability and reconstruction.

The fighting in Helmand province illustrated the difficulties American troops face in coping with well-armed factional commanders.