A suicide bomber detonated his explosives near a police checkpoint and a bank in southern Afghanistan, one of two attacks in the heartland of the insurgency that killed 18 people over 24 hours.

Separately, a Nato service member was killed by insurgents in the country’s east, according to a military statement.

No group immediately claimed responsibility for any of the attacks, but Taliban fighters have escalated their activity as US-led foreign forces reduce their presence in the country, having handed over primary responsibility for security to Afghan troops.

Javed Faisal, a spokesman for the provincial Governor, initially said the suicide bomber was in a car that was being searched by police, but later said new information indicated the bomber had been on foot. Along with the branch building of the New Kabul Bank, several small shops and vehicles were damaged.

Witness Shah Wali had just stepped out of a taxi to go to the bank when the attacker struck. “I saw a man and a vehicle on the road, and while I was fixing my shoelaces I heard a loud explosion. I don’t know if it was the vehicle which exploded or the man standing there,” Mr Wali said.

Mr Faisal said at least six people died – four of them civilians, one police officer and one private security guard. Another 24 people were wounded, most of them civilians.

Omer Zwak, a spokesman for the provincial Governor, said 11 men and one woman died in the attack, and that the vehicle also was hit by several rounds of gunfire. Such attacks typically target security forces, but, in this case, “the victims are all civilians and had no link with the government,” he added.

Afghan and coalition officials have warned that the Taliban would intensify the tempo of their attacks following the Muslim holy month of Ramadan.