KABUL, AFGHANISTAN — The weekend suicide bombing of a NATO convoy that killed 17 people in Kabul adds urgency to the U.S.-led coalition’s work to expand a security bubble around the Afghan capital.

With most of the attacks in Kabul blamed on the Pakistan-based Haqqani network, the latest reinforced U.S. and Afghan demands that Islamabad do more to curb militant activity and sanctuaries on its territory.

While there is no specific information linking Saturday’s convoy attack to the Haqqani network, investigators say they soon will have evidence the bombing was “Haqqani-related,” a western diplomat said Sunday. The diplomat, who spoke on condition of anonymity to discuss the investigation, said it was “very possible” the attack was the work of Haqqani fighters, who have ties to both al-Qaida and the Taliban.

In the brazen midday assault, a suicide bomber rammed a vehicle packed with explosives into an armored coalition bus traveling in the southwest end of the city. Heavily armored military vehicles also were in the convoy, but the bomber targeted the bus, which was carrying troops and civilians contractors.

The Haqqanis were the specific focus of two military operations this month that involved tens of thousands of Afghan and NATO troops. They were conducted over nine days in Kabul province, Wardak, Logar and Ghazni provinces south and west of the capital and Paktia, Paktika and Khost provinces along the border. More than 200 insurgents were killed or captured. At least 20 of them had ties to the Haqqani group, including 10 identified as leaders of the network.

Marine Gen. John Allen, the top commander of U.S. and NATO forces in Afghanistan, said in a recent interview with The Associated Press that the operations against the Haqqanis were conducted in preparation for next year’s plan to step up operations to keep insurgents from infiltrating across the Pakistani border and into the capital, especially from the south.

“The campaign plan is to extend operations down in that area — pretty significantly — to secure the orbital districts around Kabul and push that security zone out,” Allen said.

“The overarching campaign plan for next year is going to see us consolidate our holdings in the south, conduct operations in the east to expand the security zone around Kabul and then connect the two,” he said. That also would facilitate travel along a highway connecting Kabul with southern Afghanistan, he said.

In Saturday’s attack, the force of the explosion knocked the bus on its side and ignited a large fire that sent heavy black smoke rising above the scene. Seventeen people died — five NATO service members, including one Canadian soldier; eight civilian contractors, including two from Britain; and four Afghans, including a policeman.

A U.S. defense official initially said all the foreigners killed were American, but that could not be confirmed. NATO does not disclose the nationalities of those killed.