KANDAHAR, Afghanistan — A suicide bomber detonated his explosives near a police checkpoint and a bank in southern Afghanistan on Saturday, one of two attacks in the heartland of the insurgency that killed 18 people during 24 hours.
Separately, a NATO service member was killed by insurgents in the country’s east, a military statement indicated.
No group immediately claimed responsibility for any of the attacks, but Afghan President Hamid Karzai blamed the bombings on the Taliban. The militants have escalated their activity as US-led foreign forces reduce their presence in the country and are in the final phase of handing responsibility for security to Afghan troops.
Karzai said the militants should stop taking orders from foreigners — a veiled reference to Pakistan, whose intelligence services are alleged to be in league with the Afghan Taliban. He said the security transition is nearly done and the militants were desperate to derail it.
‘‘Taliban leaders and commanders must understand that with such crimes they will achieve nothing, but only be hated and disgust the people and God,’’ Karzai said. ‘‘They must be accountable for the Muslim nation of Afghanistan.’’
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. The bank, several shops, and vehicles were damaged.
Witness Shah Wali had just stepped out of a taxi 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,’’ Wali said.
Faisal said at least six people died — four civilians, one police officer, and one security guard. Another 24 people were hurt, most of them civilians.
Taliban spokesmen did not immediately respond to requests for comment. The militant group is especially strong in southern Afghanistan, which is dominated by the ethnic Pashtun community whose members form the bulk of the insurgency in the country.
Another 12 people were killed in an ambush involving a roadside bomb in Sangin district in Helmand province, also in the south, on Friday evening, said Omer Zwak, a spokesman for the provincial governor. Sangin is the scene of an ongoing operation by Afghan forces against the Taliban.
Zwak 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,’’ Zwak said.
On Saturday evening, a handful of insurgents attacked a police compound in Qalat, a city in southern Zabul province. The insurgents then holed up in a nearby house, under siege from security forces, said Mohammad Jan Rasoolyar, the province’s deputy governor.
Rasoolyar said one police officer and one militant were killed in the fighting, while three police officers were wounded. But as of Saturday night, the standoff was still ongoing, and Rasoolyar said the situation presented a challenge for Afghan security forces because women and children were also in the home taken over by the militants.
The official described the militants as Taliban fighters.
Afghan and coalition officials have warned that the Taliban would intensify the tempo of their attacks after the Muslim holy month of Ramadan, as they try to take advantage of the two or three months left of good weather before the harsh Afghan winter sets in.