[David]

KANDAHAR, Afghanistan (Reuters) – Unidentified gunmen shot dead a government official in southern Afghanistan on Tuesday and U.S.-led forces killed five militants south of the capital, a senior police official and the U.S. military said.

Violence has surged in the war-torn country with some 3,800 people -- a third of them civilians -- killed by the end of July this year, the United Nations said.

Dost Mohammad Arghestani, head of the social affairs department in Kandahar province, was killed on his way to work on Tuesday morning by two gunmen on a motorbike, Kandahar police chief Matiullah Qateh told Reuters.

The gunmen also killed Arghestani's bodyguard and wounded his driver, he said.

Kandahar is one of the main strongholds for Taliban Islamist insurgents, but drug smugglers, criminals and some tribal rivalries have also contributed to violence.

Separately, U.S.-led soldiers killed five militants in an operation targeting a network for foreign fighters in Rashidan, Ghazni province on Monday, the U.S. military said.

"The operation in Rashidan District targeted a Taliban subcommander who was believed to have coordinated direct attacks against Afghan and coalition forces," it said.

The coalition force killed five militants, including the subcommander, after they tried to attack the soldiers, it said.

In another incident, a Nepali working as a cook for the International Security Assistance Force (ISAF) was kidnapped along with six Afghan colleagues in western Herat on Monday night, the district governor told Reuters.

Four were later released, but Taliban commander Ghulam Yahya Siwoshani told Reuters the militant group were holding the rest and they were in good health.

Siwoshani did not say why they were keeping the men and did not make any demands.

Kidnapping has become a lucrative business in Afghanistan, where dozens of locals and foreigners have been abducted by criminals or Taliban-linked militants.

Ousted from power in 2001, Taliban insurgents have been behind a number of kidnappings in Afghanistan. Some have been killed, but most of the victims have been released unharmed.