Islamabad accuses Iran of violating its airspace in an attack on the armed group Jaish al-Adl and summons the ambassador.
Pakistan said two children were killed and three others injured after neighboring Iran launched airstrikes that Islamabad described as a violation of its airspace.
Pakistan said it had summoned Tehran's top diplomats over the incident in Islamabad.
Social media accounts reported explosions in the mountainous province of Balochistan, where the two countries share a nearly 1,000 km-long, sparsely populated border.
“This violation of Pakistan’s sovereignty is completely unacceptable and may have serious consequences,” Pakistan’s foreign ministry said in a statement.
It said the strike late Tuesday “resulted in the death of two innocent children and the injury of three girls.”
Iran's state media previously reported that Tehran had attacked two bases of the armed group Jaish al-Adl in Pakistan. The IRNA news agency and state television reported that rockets and drones were used in the attacks. Press TV, the English-language arm of Iranian state television, attributed the attack to Iran's paramilitary Revolutionary Guards. There was no official comment from Tehran.
Jaish al-Adl, the “Army of Justice,” has carried out deadly attacks against Iranian border guards since at least 2013 and has previously claimed bombings and kidnappings of border police officers.
Iran's Nournews news agency, linked to the country's top security agency, said the bases were in Balochistan province.
The Pakistani statement did not mention the location of the incident, but two Pakistani security officials told The Associated Press that the Iranian strikes damaged a mosque in Balochistan's Panjgur district, about 50 km (30 miles) inside the border. The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Tehran and Islamabad often accuse each other of allowing armed groups to operate from each other's territory.
“Pakistan has always said that terrorism is a common threat to all countries in the region that requires coordinated action,” the foreign ministry statement said.
“Such unilateral actions are not in line with good neighborly relations and can seriously undermine bilateral trust.”
On Monday, Iran fired missiles into northern Syria that targeted the IS group (ISIS) and a so-called Israeli “spy headquarters” near the US consulate in the city of Erbil, Iraq.
Iraq on Tuesday called the attacks that killed several civilians a “flagrant violation” of Iraqi sovereignty and recalled its ambassador from Tehran.