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.
The artillery fire came after clashes between Pakistani and Afghan security forces at the closed Chaman-Spin Boldak border crossing, where crowds on both sides were waiting to cross for the Muslim festival of Eid al-Adha.
"If the Pakistani military continues its rocket attacks on Afghan territory, they will face retaliation by the Afghan army," Afghanistan's defense ministry said in a statement.
Pakistan's foreign office and military did not immediately respond to Reuters' requests for comment, but Foreign Minister Shah Mahmood Qureshi told reporters that the matter had been taken up with Afghan authorities and hoped it would be resolved amicably.
Pakistan and Afghanistan are both US allies but their relations have rarely been close.
Afghanistan has for years accused Pakistan of supporting Taliban militants. Pakistan denies doing so and in turn accuses Afghanistan of supporting militants fighting the Pakistani government.
The governor of the southeastern Afghan province of Kandahar, Hayatullah Hayat, said the shells fell in residential areas of Spin Boldak and that women and children were among the 15 dead and 80 wounded.
Hospital officials in Pakistan told Reuters three bodies and 20 people suffering bullet wounds had been brought after the clashes between protesters and security forces.
They exchanged fire when crowds waiting to cross into Afghanistan became unruly and attacked Pakistani installations, a Pakistani official said.
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 center 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.