QUETTA: Backed by artillery, Afghan security forces fired across the border on Pakistani census workers and troops escorting them on Friday, killing nine and drawing a response from the military, Pakistan said. On the Afghan side, officials reported six killed in the incident, a significant escalation of hostilities between the two neighbors.

Pakistani government and military officials said the artillery rounds that hit in the border town of Chaman in southwestern Baluchistan province were unprovoked but Afghan provincial officials claimed that the Pakistanis fired first.

The incident was the latest escalation between the two neighbors who share a volatile and porous boundary.

Pakistani army spokesman Maj. Gen. Asif Ghafoor said the army shut the border crossing in Chaman in response to the early morning attack, blocking all movement of people and supplies to its landlocked neighbor.

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.

At least 42 people were reported wounded on the Pakistani side, including women and children, and Mohammad said some of the wounded were in critical condition.

Prime Minister Nawaz Sharif issued a statement describing the Afghan firing as "unfortunate" and urged Kabul to put an end to cross-border attacks that threaten efforts to bring peace to Afghanistan.

Pakistan's foreign ministry 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.

Gen. Abdul Raziq, 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. Raziq said six people — four Afghan policemen and two civilians — were killed while another 37 were wounded by Pakistani forces' fire. Among the Afghan wounded were 23 civilians.

"Pakistani forces were trying to infiltrate Afghan territory but Afghan forces stopped them; that's when the fight started," said Raziq.

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

Pakistan and Afghanistan routinely accuse each other of providing sanctuaries to their enemy insurgents — something both sides deny. Despite several high-level visits by Pakistani intelligence and security officials to Afghanistan in recent weeks, relations between the two countries continue to deteriorate.

Gen. Ghafoor also 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.

Later Friday, the Pakistani military said a hotline had been established between the two sides and that the cross-border shooting had stopped.

Pakistani Maj. Gen. Sahir Shamshad Mirza asked the Afghan military to ensure its forces stay on their side and take every step to "defuse the situation" while the Pakistani military would "work within our own border."

Pakistan shares a 2,200-kilometer- (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 censor-takers going door-to-door to collect information.

The census — the country'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 Pashtun 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.