Tehran denied the allegation and blamed Israel, Azerbaijan's ally, of trying to stage a provocation.

The midday attacks involved at least four drones that crossed from Iran into Azerbaijan's exclave of Nakhichevan bordering Iran, Baku said.

"Today a terrorist act was carried out from the Iranian side against the territory of Azerbaijan," Aliyev told a hastily convened security council meeting.

Azerbaijan's military "have been instructed to prepare and carry out retaliatory measures ... placed on mobilisation level number one, and must be ready to conduct any operation," he said.

"Those dishonourable people who committed this terrorist act against us will regret it. Let them not test our strength... This stain will never be erased from their dirty and ugly face," he added.

The Azerbaijani defence ministry said it had detected four drones launched by Iran's army.

"One of them was disabled by the Azerbaijani army, while the others were directed at civilian infrastructure, including a secondary school building during class hours. Fortunately, the drone targeting the school did not reach its objective and instead fell and exploded near the school," it said.

The Nakhichevan Airport terminal was damaged, the foreign ministry said, with video showing grey smoke rising above the building after the strike.

Four people were hospitalised with "traumatic brain injuries," Sahib Abuzarov, head of emergency services at a hospital in Nakhichevan said later.

The general staff of Iran's armed forces said it did not carry out the attack and pointed the finger at Israel.

"Such actions by the Zionist regime, aimed at disrupting relations between Muslim countries in various ways, are not unprecedented," it said in a statement.

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Turkey's foreign ministry condemned strikes "which target third countries in the region and increase the risk of the war spreading," adding it "will continue to stand by Azerbaijan, as it always has".

Azerbaijan's foreign ministry summoned the Iranian envoy in Baku to express "strong protest" over the attack, which it said "contradicts the norms and principles of international law and contributes to rising tensions in the region".

"We demanded from the Islamic Republic of Iran to provide, within the shortest possible timeframe, a clear explanation regarding the case and conduct investigation," Azerbaijani foreign ministry spokesman, Aykhan Hajizada, told AFP.

Analysts have said Azerbaijan's Baku-Tbilisi-Ceyhan oil pipeline -- which runs through neighbouring Georgia and Turkey and carries around a third of Israel's oil imports -- could become a potential target for the Iranian military.

In 2024, Azerbaijan exported 2.37 million tonnes of oil to Israel via Baku-Tbilisi-Ceyhan, director of the Baku-based Centre for Oil Research, Ilham Shaban, told AFP.

"The pipeline is buried underground along most of its route, making it difficult to disable," he said, adding that "above-ground facilities -- such as terminals and pumping stations -- could still be vulnerable to Iranian drone strikes."

Iran has long expressed concern that Israel -- a close ally of Azerbaijan and a key arms supplier -- could use Azerbaijani territory to stage attacks.

Last June, Azerbaijan reassured Iran that it would not allow its territory to be used for attacks against Tehran after Israel launched a large-scale strike on Iranian targets.

Tehran has historically been wary of separatist sentiment among its ethnic Azerbaijani minority, which makes up around 10 million of Iran's 83 million citizens.