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

A public funeral was held for Ismail Haniyeh, Hamas' politburo chief, in the Iranian capital on Thursday where he was killed early on 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 was laid to rest on Friday.

Iran's First Vice President Mohammad Reza Aref and Turkish Foreign Minister Hakan Fidan were among the officials who attended Haniyeh's funeral.

The New York Times, citing Middle Eastern officials, reported that Haniyeh was killed by an explosive device planted several weeks ago at a Teheran guesthouse.

Asked about the report, Israeli military spokesman Daniel Hagari told journalists "there was no other Israeli aerial attack … in all the Middle East" on the night of Fuad Shukr's killing in Lebanon.

Hours before Haniyeh's killing on Wednesday, Shukr, Hezbollah's senior military commander, was killed in an Israeli strike on Lebanon's capital Beirut.

Hezbollah chief Hassan Nasrallah, on Thursday, said that 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.

Israel said Shukr's assassination was a response to deadly rocket fire last week on the Israeli-occupied Golan Heights.

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

The leader of Yemen's Houthi militants also vowed a "military response" to Israel's "major escalation".

Qatar-based network Al Jazeera reported that the plane carrying Haniyeh's body had landed in Doha, before Haniyeh was buried.

"How can mediation succeed when one party assassinates the negotiator on the other side?" Sheikh Mohammed bin Abdulrahman Al Thani said on social media site X.

Hugh Lovatt, an analyst at the European Council on Foreign Relations, also said Haniyeh's killing, at the very least, "will mean that a cease-fire deal with Israel is now totally off the table".

US President Joe Biden said late on Thursday he was "very concerned" about rising tensions in the region, adding that the killing of Haniyeh had "not helped" the situation.

As concerns grow over a possible conflict in the region, airlines are avoiding Iranian and Lebanese airspace and canceling flights to Israel and Lebanon.

Flights canceled

Singapore Airlines on Friday appeared to no longer be using Iranian airspace for any of its routes, according to flight tracker Flightradar24. The airline did not respond to a request for comment.

The international community has called for calm and a focus on securing a cease-fire in the Gaza Strip, which Haniyeh had accused Israel of obstructing.

In Tel Aviv, hundreds of Israelis marched to demand the return of hostages, as they endured their 300th day of captivity in Gaza on Thursday.

"There is no victory until the hostages are back," chanted the demonstrators, near the defense ministry in the country's commercial hub, an AFP correspondent reported.