Kabul - Two civilians were killed and 25 others injured when a Taliban rocket hit a bus in southern Afghanistan, while Afghan and NATO-led forces killed at least eight militants elsewhere in the country, officials said Wednesday.

Taliban militants attacked a logistics convoy in the Qara Bagh district of the southern province of Ghazni on Tuesday evening, but one of their rockets hit a passenger bus, which was travelling on the Kabul-Kandahar highway, Khailbaz Shirzai, the provincial police chief said.

"Two male passengers were killed and 25 others were wounded in the attack," he said, adding, "Some of the wounded people are in critical condition."

He said three members of a private security firm, who were guarding the convoy, were also injured in the attack.

The attack came a week after 30 Afghan civilians were killed and nearly 40 other passengers were injured when a bomb tore through a bus close to Kandahar city in the country's southern region.

The Taliban's homemade bombs, which are aimed at Afghan and NATO-led forces in the country, often kill or injure civilians, who have borne the brunt of insurgent attacks in the past eight years since the fall of the Taliban's hardline Islamist regime.

About 1,500 Afghan civilians were killed from January to August, up 20 per cent from the same period last year, according to a United Nations report. Around two-thirds of those were killed by insurgents while most of the other 30 per cent were killed by NATO airstrikes.

Meanwhile, clashes between Taliban militants and Afghan forces backed by NATO troops continued throughout the country.

Five militants were killed and four others arrested by Afghan and US troops in the Sayedabad district, Wardak province, on Wednesday, Shahidullah Shahid, spokesman for the provincial governor, said.

The US military also confirmed the incident in a statement, saying the soldiers killed and arrested several militants, who were responsible for roadside bomb attacks in the area. "The joint force also found a suicide vest and destroyed it in place," it said.

Three others militants were killed in southern province of Zabul on Tuesday, the Afghan Defence Ministry said, while several other militants were killed in Kabul, Helmand and Khost provinces since Tuesday, a US military statement said.

Taliban-led violence is on the rise in the country as militants are believed to have infiltrated previously relatively peaceful regions.

More than hundred militants were killed in a battle in the eastern province of Nuristan over the weekend, according to NATO.

The clash happened after the militants attacked two remote outposts in the province. The daylong firefight also left eight US soldiers and two Afghan troops dead.

The provincial governor said that another 30 militants were killed on Monday when the combined forces began an operation to root out militants from the area. (dpa)