More than 30 Taliban fighters and four policemen were killed in a series of clashes, airstrikes and bombings in Afghanistan, officials said Wednesday.

Taliban fighters attacked a police checkpoint in the Nad Ali district of southern Helmand province Tuesday, sparking a clash that killed 18 militants, provincial police chief Mohammad Hussein Andiwal said.

The militants attacked the officers guarding a government compound in the district before being repelled by the police, Andiwal said. There were no casualties among Afghan troops, he said.

The militants have attacked the same checkpoint many times in the past, and the authorities had reinforced their position, Andiwal said.

U.S.-led coalition troops, meanwhile, clashed and called in airstrikes on another group of militants in the same province killing over a dozen insurgents, the coalition said in a statement.

Shortly before the battle, the coalition troops spotted armed militants in small groups preparing to attack their patrol in Sangin district, the statement said. There were no coalition casualties from the clash.

Southern Afghanistan is the center of the Taliban-led insurgency, which has also spread in the country's east.

Separately, a roadside bomb in the central Ghazni province hit a police vehicle, killing four officers on Tuesday, said Sayed Ismail Jahangir, a spokesman for the provincial governor.

A suicide bomber, meanwhile, blew himself up next to a British military patrol outside Lashkar Gah on Tuesday, wounding three civilians, Andiwal said.

NATO-led force said they had no casualties from the bombing.

More than 3,500 people — most of whom militants — have died in insurgency-related violence so far this year according to an Associated Press tally of figures provided by Afghan and Western officials.