The war in the Middle East has spilled over Iran's northern border, with Azerbaijan saying Iranian drones struck its Nakhchivan exclave on Thursday, the BBC reports.

The airport terminal was hit, a drone exploded near a school, injuring civilians, and another drone was shot down.

Azerbaijan's President Ilham Aliyev condemned the incident as an "act of terror", demanded an explanation and apology from Tehran, while placing Baku's armed forces on high alert.

He also touched on Iran's ethnic Azerbaijani population—a sensitive subject for Tehran.

Iran denies any role in Thursday's strikes and has suggested the attack may have been an Israeli false flag operation.

But Aliyev’s anger went beyond words, saying that "independent Azerbaijan is a place of hope for Azerbaijanis living in Iran."

Baku has long avoided this line because of how sensitive it is for Tehran.

Iran is home to an estimated 20-25 million ethnic Azeris, who make up its largest minority group and are concentrated in the northwest along the Azerbaijan border.

The Islamic Republic has consistently regarded their identity and political affiliations as issues of utmost sensitivity. 

Aliyev has rarely spoken about Iranian Azeris in such explicitly aspirational terms and doing so now appears to be a calculated move.

Aliyev's message comes across as a warning to Tehran: any attempt to pressure Azerbaijan militarily or diplomatically could result in a response from Baku, including one that affects Iran's internal stability.

Aliyev's decision to talk openly of Azerbaijan being a "place of hope" for Iranian Azeris introduces a new and potentially unpredictable element, the BBC added.