Israel will respond forcefully to any attack on it, Prime Minister Benjamin Netanyahu said on Wednesday, after the killing of Hamas leader Ismail Haniyeh in Tehran and of a senior Hezbollah leader in Beirut.

Netanyahu said Israel had delivered crushing blows to Iran's proxies over the past few days, including Hamas and Hezbollah. But he did not mention Haniyeh's killing, which has drawn threats of revenge on Israel and fuelled further concern that the conflict in Gaza was turning into a wider Middle East war.

"Citizens of Israel, challenging days lie ahead. Since the strike in Beirut there are threats sounding from all directions. We are prepared for any scenario and we will stand united and determined against any threat. Israel will exact a heavy price for any aggression against us from any arena," Netanyahu said in a televised statement.

Israel's military announced late on Tuesday it had killed Fuad Shukr, whom it named as Hezbollah's most senior commander and whom it blamed for an attack at the weekend that left a dozen youngsters dead in the Israeli-occupied Golan Heights.

Shukr was an adviser to Hezbollah leader Sayyed Hassan Nasrallah, according to Hezbollah sources and to Israeli officials.

Iran-backed Hezbollah confirmed his death on Wednesday, hours after the Palestinian armed group Hamas announced its leader, Haniyeh, had been assassinated in Teheran.

Although the Tehran attack was widely assumed to have been carried out by Israel, Netanyahu's government made no claim of responsibility and said it would make no comment on Haniyeh's killing.