Iran says it has hit a militant group in western Pakistan in a missile attack, its third air strike on another country this week after earlier attacks on targets in Iraq and Syria.
The operation hit two sites in Balochistan linked to the militant group Jaish al-Adl, Iranian state TV said.
Pakistani officials said two children were killed and three others injured.
Islamabad said the air strike was an "illegal act" and warned it could lead to "serious consequences".
The latest air strike comes at a time of growing tension across the Middle East, with more than 100 days of war between Israel and the Palestinian group Hamas in Gaza and recent US-UK air strikes on Yemen, from where Iran-backed Houthi militants have been attacking commercial shipping in the Red Sea.
China on Wednesday urged Pakistan and Iran to show "restraint" and "avoid actions that would lead to an escalation of tension".
Tuesday's strike in Pakistan hit a village in the vast south-western border province of Balochistan. Tehran said it was targeting Jaish al-Adl, or "army of justice", an ethnic Baloch Sunni Muslim group that has carried out attacks inside Iran as well as on Pakistani government forces.
Yet both have accused one another of harboring militant groups that carry out attacks on the other in their border areas for years.
Tehran has linked Jaish al-Adl with attacks last month close to the border, which killed more than a dozen Iranian police officers.
Jaish al-Adl is the "most active and influential" Sunni militant group operating in Sistan-Baluchestan, according to the office of the US Director of National Intelligence.
