Clashes have erupted between Pakistan's border forces and people trying to cross into Afghanistan for the Muslim festival of Eid al Adha.

Cross-border artillery fire by Pakistan killed at least 15 civilians in Afghanistan on Thursday, Afghan officials said, prompting Kabul to put its ground and air forces on alert.

Differing accounts emerged from Kabul and Islamabad, with Afghan officials accusing Pakistan of firing shells and gunfire across the border into a crowd of civilians, killing 15 people.

The incident unfolded on Thursday when about 150 people gathered on the Pakistani side of the Chaman-Spin Boldak border crossing, many of them hoping to visit loved ones in Afghanistan for Eid al Adha, Usman Ali, the commissioner for the Quetta border region, said.

The normally busy crossing has been largely closed for months in a bid to slow the spread of the coronavirus, but was briefly opened on Thursday morning. 

'Frontier Corps troops deployed'

Ali said protesters grew angry when the crossing point was again closed in the afternoon. 

"Frontier Corps troops deployed on the border fired into the air. This did not kill anyone but later protesters started throwing stones at the troops," Ali said. 

He claimed the border guards then threw stones back, killing five protesters. He denied the guards had opened fire on people.

'Shelling and sporadic firing'

On the Afghan side meanwhile, Baheer Ahmad, a spokesman for the Kandahar provincial governor, said that 15 people had been killed and 80 others wounded "as a result of shelling and sporadic firing by the Pakistani border forces."

One policeman was among the dead, with the rest of the casualties civilians, he said. 

Afghan Defence Ministry spokesman Fawad Aman said on Facebook that "attacks by the Pakistani military on Afghan soil on Thursday" had killed nine civilians and wounded 50 others. 

"If the Pakistani military continues its rocket attacks on Afghan territory, they will face retaliation by the Afghan army," Afghanistan's Defence Ministry said in a statement.

Pakistan's Foreign Ministry and border force did not respond to multiple requests for comment. 

Tensions are high between Pakistan and Afghanistan, with Kabul frequently lashing out at Islamabad for allegedly sheltering, funding and supplying the Taliban. 

Pakistan denies the claims. 

READ MORE:UN: Thousands of anti-Pakistan militants hiding in Afghanistan

Tense situation continues

The crossing, mostly closed to pedestrians during the Covid-19 pandemic, was briefly opened on Wednesday and was to open again Thursday to allow nationals of both countries to cross for Eid, which falls on Friday in Afghanistan and Saturday in Pakistan.

When it did not open, a large crowd gathered to protest, and a quarantine centre and a Pakistani government facility for processing movement at the crossing were burned down, a Pakistani official at the border told Reuters.

An official of the Chaman administration, Zakaullah Durrani, told Reuters that the situation on the border remained tense.

READ MORE: Economy forces Pakistan to reopen even as Covid-19 cases spike