Updated

Taliban insurgents dressed in police uniforms and driving in a police car attacked a checkpoint in southern Afghanistan's restive Helmand province on Wednesday, killing 14 police officers, an Afghan official said.

The attack, the latest in a stepped-up campaign by the Taliban targeting Afghan forces and government institutions, underscores the tenaciousness of their insurgency even as the group is plagued by infighting and rivalries following last month's announcement of the death of its longtime leader, Mullah Mohammad Omar.

In Wednesday's attack, Taliban fighters drove through the checkpoint in the district of Musa Qala and attacked the police officers from behind, according to Bashir Ahmad Shaker, a provincial council member in Helmand.

Helmand Gov. Mirza Khan Rahimi said two other policemen were wounded in the attack, which he called it a "conspiracy against the police."

Rahimi said the police were caught unprepared because an earlier telephone call had informed them to expect a visit from police colleagues. "But the visitors were attackers in police uniforms who opened fire and killed them," Rahimi said, adding that an investigation is underway.

Taliban spokesman Qari Yusouf Ahmadi claimed responsibility for the attack and said the insurgents had captured eight policemen.

In Kabul, Afghanistan's intelligence agency claimed on Wednesday that Pakistan was involved in last week's attacks in the country's capital that killed almost 50 people and wounded hundreds.

Hassib Sediqi, the spokesman for the National Directorate of Security, said that Afghan authorities have confirmed "Pakistani military interference" in the attacks last Friday.

"Special circles of the Pakistani military were behind all those attacks," Sediqi said, claiming the Pakistanis were working through the Haqqani network, one of the most vicious militant groups in Afghanistan.

There was no immediate reaction from Islamabad, which has in the past denied such accusations from Kabul. Pakistan wields considerable influence over the Taliban, which have waged a 14-year war against Kabul.

Three attacks last week shocked Kabul in their scope and brutality. A truck bomb exploded early Friday morning, flattening a city block and killing 15 people and wounding 240 as they slept, authorities said.

Hours later, a suicide bomber killed at least 20 cadets outside a police academy, while another 10 people died in an attack on a military camp used by U.S. Army Special Forces. On Monday, an attack near Kabul's airport killed five people.

The Taliban claimed responsibility for most of the attacks.

"Suicide bombers are receiving their training in Pakistan, there are factories in Pakistan that are making bombs and explosives, which are used to kill and wound civilians in Afghanistan," Sediqi said.

He claimed "it has been proved that the Taliban" are not led by Afghans but are getting "their orders form the Pakistani military officers."

Earlier on Wednesday, Afghan authorities recovered the bodies of four men kidnapped in the country's east last week, officials said, while at least eight others have been newly abducted.

The four bodies, found in Nawur district near the Pakistani border, all had been shot dead, said Asadullah Ensafi, the deputy chief police of Ghazni province. He said three of the men were Hazara, while the fourth was a Sunni Pashtun.

The Hazara are a largely Shiite ethnic minority in predominantly Sunni Afghanistan. The group has been targeted by the Taliban and other Sunni extremists in Afghanistan and neighboring Pakistan.

Ensafi said insurgents kidnapped another at least eight Hazaras on Tuesday. In February, 30 Hazara men were abducted in Zabul province, south of Ghazni. Last month, 11 Hazaras were kidnapped in northern Baghlan province, which also has been plagued by militants since the Taliban stepped up their war against Kabul in April.

Meanwhile, fighting in Baghlan between Afghan forces and the Taliban has killed two police officers, said Jaweed Basharat, the provincial police spokesman. He said the fighting in the Dahana-I-Ghori district began on Tuesday. The Taliban, who regularly exaggerate their claims, issued a statement, claiming a much higher police casualties figure.