US-led coalition and Afghan forces have killed more than 100 Taliban in the southern Afghan province of Helmand during three days of fighting, the US military has said in a statement.

The fighting began after patrols came under attack from small arms, rocket propelled grenades and mortars in the southwestern province, the US military said in a statement on Thursday.

The patrols returned fire and called in close-air support, it said.

"Heavy casualties were inflicted during fierce fighting between Afghan soldiers and insurgents, but the exact number of casualties is not known," the Afghan defence ministry said.

Violence has surged in Afghanistan with more than 2,500 people, including 1,000 civilians, killed in the conflict in the first six months of this year, according to aid agencies.

Mainly British troops have been engaged in fighting with Taliban fighters in Helmand province for three years.

Opium crop

The province is home to two-thirds of Afghanistan's opium crop, the raw ingredient of heroin, and the site of frequent clashes involving local Taliban fighters.

In the southern province of Zabul a day earlier, 12 Taliban fighters were killed and six wounded by Afghan and US-led soldiers in clashes in the district of Arghandab, the Afghan defence ministry said in a statement.

The ministry also said Afghan soldiers killed 10 Taliban fighters in Helmand's Girishk district the same day.

One Afghan soldier was killed and another wounded during the fighting, which was part of a larger operation aimed at finding drug traffickers in the area, officials said.

One US-led coalition soldier was killed while on patrol on Wednesday in southern Afghanistan, the US military said in a statement.