Iran said its retaliation for the assassination of a top Hamas official by Israel will be “definitive”, as fears of a major escalation of hostilities in the Middle East continue to grow.

Israel has been accused by Iran of assassinating Ismail Haniyeh, the political leader of Hamas, at the beginning of August while he was in Tehran to attend the inauguration of the country’s new President Masoud Pezeshkian.

The killing, for which Israel hasn’t publicly acknowledged responsibility, provoked a furious response from Tehran, who vowed to avenge Haniyeh’s death at all costs.

Western governments have attempted to persuade Iran against a punitive strike on Israel, fearing it could lead to a major escalation of hostilities in the region.

Over the weekend, Italy’s Foreign Minister Antonio Tajani spoke to his Iranian counterpart in ongoing diplomatic efforts to ease tensions.

However, Iran insisted it would carry out its retaliation and did not fear the consequences.

Abbas Araghchi, Iran’s Foreign Minister said: “Iran reaction to Israeli terrorist attack in Tehran is definitive, and will be measured and well calculated.”

“We do not fear escalation, yet do not seek it – unlike Israel.”

In a statement, Italy’s Foreign Minister Mr Tajani said he “called for restraint and to pursue a constructive approach, in order to stop the cycle of military actions in the region, which only risks bringing more suffering.”

The telephone conference between the two politicians came in the wake of a rocket and drone attack on Israel on Sunday by Hezbollah – a Shia militia backed by Iran.

Hezbollah’s leader Hassan Nasrallah said his forces fired more than 300 rockets in a retaliatory strike for the killing of its top commander Fuad Shukr in July by Israel.

Israel’s Defence Force claimed the attack caused minimal damage and said it had launched a “pre-emptive” strike against Hezbollah targets in Lebanon, after detecting moves to fire missiles into Israel.

The IDF used 100 jet fighters that hit more than 40 target sites inside Lebanon in sorties over a period of seven hours.

Israel’s Prime Minister, Benjamin Netanyahu, warned the air strikes were “not the end of the story” in its fight against Hezbollah.

Although he declined to specify exactly what further action the IDF would take, he suggested Israel’s moves would be aimed at “changing the situation in the north”.

It comes as a Hamas official said on Sunday that it rejected new Israeli conditions put forward in Gaza ceasefire talks.