Updated

A suicide bomber rammed a car packed with explosives into a police truck outside a bakery in southern Afghanistan on Tuesday, killing at least two civilians, officials said.

The attacker apparently was waiting in the car at the gates of the police headquarters just outside a bakery where officers regularly buy bread in the morning in Lashkar Gah, the main city in Helmand province, said deputy provincial Police Chief Kamaluddin Sherzai. The bomber the slammed into a police truck that was parked at the shop, triggering the car's explosives, he said.

Two civilians -- one man and one young boy -- were killed in the blast, said provincial government spokesman Daoud Ahmadi. Another 26 people were wounded, including 10 police officers and six children, he said.

Taliban spokesman Qari Yousef Ahmadi claimed responsibility for the attack, which came hours after the Taliban released a formal statement rejecting claims that the insurgency has become splintered or that the group or any of their allies have ties to the Pakistani government.

The statement said the Taliban insurgency "is at its strongest and unified more than it has been at any other stage," and denied that the movement has bases in Pakistan.

The claim runs contrary to U.S. and international assertions that the Taliban retain numerous safe havens and bases in Pakistan's tribal areas, used to stage attacks into neighboring Afghanistan.

The Taliban also reject U.S. charges that the Haqqani network, a key affiliate, has ties to Pakistan's intelligence service. The group says Haqqani network founder Jalaluddin Haqqani is a key member of the Taliban leadership.

The Taliban statement appeared to be an attempt to give the Pakistani government some breathing room as Islamabad comes under increasing pressure to take action against insurgents within its borders.

In the wake of three major attacks in the Afghan capital in the past two weeks, U.S. officials have ramped up their public comments alleging the Pakistani government backs the Haqqani network, which is believed to be behind a number of attacks in and around Kabul. The Afghan government, meanwhile, has upped its protests against cross-border artillery attacks it blames on Pakistan.

On Monday, the Afghan government said that Afghan-Pakistan relations will suffer if the attacks in eastern Afghanistan continue.

A NATO forces spokesman said Monday that the Haqqani network is still very much operating out of Pakistan.

"We have no credible intelligence indicating that the Haqqani network has eliminated their operating safe havens in Pakistan," said Brig. Gen. Carsten Jacobson, a spokesman for NATO forces in Afghanistan. "They continue to plan and execute operations from across the border."

In Kabul, meanwhile, tensions between different political factions were on the rise as hundreds of demonstrators, led by former intelligence chief Amrullah Saleh, accused the government of mishandling the investigation into last week's killing of former president Burhanuddin Rabbani.

Saleh told the assembled group that international officials should investigate the assassination rather than the Afghan government. He said that he did not trust Afghan officials to conduct an honest investigation.