Backed by artillery, Afghan security forces fired across the border on Pakistani census workers and troops escorting them, killing 11 civilians and wounding 46, including women and children, Pakistani officials said Friday.

The Pakistani government and military officials said the artillery rounds were unprovoked but Afghan provincial officials claimed the Pakistanis fired first, wounding two Afghan policemen.

Friday’s incident in the border town of Chaman in Balochistan was the latest escalation between the two neighbours who share a volatile and porous boundary.

Army spokesman Major General Asif Ghafoor said the security forces shut the border crossing in Chaman in response to the early morning attack, blocking all movement of people and supplies to its landlocked neighbour.

Residents in the area said Pakistani and Afghan security personnel exchanged fire using light and heavy weapons.

“So far, we have received nine bodies. These civilians were killed as a result of the Afghan shelling,” said Akhtar Mohammad, a doctor at the state-run hospital in Chaman. He said some of the wounded were in critical condition.

Prime Minister Nawaz Sharif issued a statement describing the Afghan firing as an “unfortunate.” He urged Kabul to put an end to cross-border attacks, warning that they threaten efforts to bring peace to Afghanistan.

Foreign Office spokesman Nafeez Zakaria said the census workers were on their side of the border when Afghan forces opened fire.

According to local residents, dozens of shells slammed into nearby villages, as well as close to the regional headquarters of Pakistan’s paramilitary forces. Several of the wounded said their homes were destroyed in the exchange.

Yet Zia Durrani, a spokesman for the police chief in Afghanistan’s Kandahar province, blamed Pakistan for initiating the gunbattle. He accused Islamabad of using the census as a mask to conceal the crossing of militants from Pakistan into Afghanistan.

In Islamabad, the foreign ministry said it had summoned Afghanistan’s chargé d’affaires to complain about the firing.

General Ghafoor, meanwhile, accused Afghan forces of creating obstacles for census workers in villages divided by the Pakistan-Afghanistan border. He did not elaborate on what those obstacles entailed.

Pakistan shares a 2,200-kilometre- (1,375 mile-) long porous border with Afghanistan.

Pakistan currently hosts 1.5 million registered Afghan refugees and another 1 million unregistered. They routinely get caught in the middle when tensions between Pakistan and Afghanistan escalate.

Pakistan started conducting a nationwide census in mid-March, with officials going door-to-door to collect information.

The census – Pakistan’s first since 1998 - has reignited a centuries-old border dispute between Pakistan and Afghanistan. The boundary, known as the Durand Line - named for Sir Henry Mortimer Durand, the former British diplomat who first established the border in 1896 - runs through vast ethnic Pashtoon areas on both sides, in some places straight through villages.

Any attempt to make the border a permanent one has been fiercely opposed by Afghanistan. The two countries routinely squabble over the disputed border line, incidents which at times escalate into armed conflict.

In March this year former Afghan president Hamid Karzai again said that Afghanistan would never accept the Durand Line as an international border, stoking fears on the Pakistani side.