Pakistan has launched missile strikes into Iran, killing nine people, after Iran carried out strikes in Pakistan late on Tuesday.
Pakistan said its strikes had hit "terrorist hideouts" in Iran's south-eastern Sistan-Baluchestan province.
Iran condemned the attack, which it said killed three women, two men and four children who were not Iranian.
The country's foreign ministry later said it was committed to good neighbourly relations with Pakistan.
However, it called on Islamabad to prevent the establishment of "bases and armed terrorist groups" on its soil.
The reciprocal attacks come as tensions in the Middle East are high with several overlapping crises.
Israel is fighting the Palestinian group Hamas in Gaza and exchanging fire with Iran-backed Hezbollah in Lebanon.
Meanwhile, Iran-backed groups in Iraq and Syria are targeting US forces, and the US and UK have struck the Iran-backed Houthis in Yemen, who have been attacking shipping.
Thursday's strikes by Pakistan were the first external land attack on Iran since Saddam Hussein's forces invaded in the 1980s - launching a brutal eight-year war.
Pakistan's foreign ministry said its strikes around the Iranian city of Saravan had come in light of "credible intelligence of impending large-scale terrorist activities" and added that it "fully respects" Iran's "sovereignty and territorial integrity".
In its own statement, Pakistan's army said the "precision strikes" were conducted with drones, rockets and long-range missiles and targeted the Balochistan Liberation Army and the Balochistan Liberation Front.
Both groups are part of a decades-long struggle for greater autonomy in Balochistan, a remote region in south-western Pakistan.
Pakistan had fiercely condemned Iran's strike on Tuesday, which struck an area of Pakistan's Balochistan province near the Iranian border and which Islamabad said killed two children.
The country's former foreign minister, Bilawal Bhutto Zardari, told the BBC he was surprised at the attack because Iran's foreign minister met with Pakistan's acting prime minister on "the day they violated the sovereignty of our country".
He added "it would be a mistake" for a country to think Pakistan can't respond to violations, and says it sends a "clear message that Pakistan has both the will and ability to respond".
Iran insisted its strikes were aimed only at Jaish al-Adl, or "army of justice", an ethnic Baloch Sunni Muslim militant group (formerly called Jundullah) that has carried out attacks inside Iran, and not Pakistan's citizens.
Iranian state media reported on Thursday that Tehran had summoned Pakistan's chargé d'affaires over the strikes. Pakistan had earlier recalled its ambassador and blocked the Iranian envoy from returning.
China, Turkey and the Taliban government in Afghanistan have all called for restraint and dialogue.
Earlier in the week Iran also attacked targets in Iraq and Syria. It said it had hit Islamic State and Israel's Mossad spy agency, both of which it said had been involved in a bomb attack in the Iranian city of Kerman earlier this month which killed 84 people.
