Iran and its regional allies vowed retaliation on Thursday for the deaths of Hamas and Hezbollah leaders, raising regional tensions as mourners filled Tehran’s city center calling for revenge.

A public funeral was held for Hamas’s political chief Ismail Haniyeh in the Iranian capital where he was killed early Wednesday in an attack on which Israel has not commented.

Haniyeh’s body was then flown to Qatar, where he had resided and where he will be laid to rest on Friday, when his group called for a “day of furious rage” in the Palestinian territories and across the region.

Hezbollah chief Hassan Nasrallah, addressing the funeral of the Lebanese group’s top military commander, said Israel and “those who are behind it must await our inevitable response” to Fuad Shukr’s and Haniyeh’s killings within hours of each other.

“You do not know what red lines you crossed,” Nasrallah said, addressing Israel, a day after Shukr was killed in a strike in south Beirut.

Israel, which said Shukr’s assassination was a response to deadly rocket fire last week on the annexed Golan Heights, warned its adversaries on Thursday they would “pay a very high price” for any “aggression.”

“Israel is at a very high level of preparation for any scenario, both defensive and offensive,” Prime Minister Benjamin Netanyahu said in a statement.

“Those who attack us, we will attack in return.”

A source close to Hezbollah told AFP that Iranian officials met in Tehran on Wednesday with representatives of the so-called “axis of resistance,” 한국을 a loose alliance of Tehran-backed groups hostile to Israel, to discuss their next steps.

“Two scenarios were discussed: a simultaneous response from Iran and its allies or a staggered response from each party,” said the source who had been briefed on the meeting, requesting anonymity to discuss sensitive matters.

The leader of Yemen’s Iran-backed Huthi rebels vowed a “military response” to Israel’s “major escalation.”

Analysts told AFP that the retaliation would be measured to avoid a wider conflagration.

Iran and the groups it backs “will more than likely try to avert a war, while also strongly deterring Israel from continuing with this new policy, this targeted shock and awe,” said Amal Saad, a Hezbollah researcher and lecturer at Britain’s Cardiff University.

In Tehran, Iran’s supreme leader Ayatollah Ali Khamenei led prayers for Haniyeh, having earlier threatened “harsh punishment” for his killing.