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Iran has dismissed calls from the UK and other Western countries to refrain from retaliation against Israel for the killing of Hamas leader Ismail Haniyeh in Tehran last month.

Amid a flurry of international diplomacy to de-escalate tensions, UK Prime Minister Keir Starmer urged Iranian President Masoud Pezeshkian to “stand down its ongoing threats of a military attack” in a rare telephone conversation on Monday.

But Pezeshkian said retaliation was a “way to stop crime” and Iran’s “legal right”, according to Iranian state media.

Israel, which did not say it was involved in Haniyeh’s assassination, has meanwhile put its military on its highest alert level.

The US has warned that it is preparing for “a significant set of attacks” by Iran or its proxies as soon as this week, and has built up its military presence in the Middle East to help defend Israel.

The powerful Iran-backed Hezbollah movement in Lebanon is also threatening to retaliate over Israel’s killing of one of its top commanders in an air strike in Beirut.

On Monday evening, the leaders of the UK, France and Germany issued a joint statement urging Iran and its allies to “refrain from attacks that would further escalate regional tensions”.

“They will bear responsibility for actions that jeopardise this opportunity for peace and stability,” Sir Keir, President Emmanuel Macron and Chancellor Olaf Scholz said.

Later, the British prime minister also expressed his deep concerns directly to Iran’s president by telephone – the first such call since March 2021.

Sir Kier told Pezeshkian that “there was a serious risk of miscalculation and now was the time for calm and careful consideration”, Downing Street said.

“He called on Iran to refrain from attacking Israel, adding that war was not in anyone’s interests,” it added.

On Tuesday morning, Iranian state news agency Irna reported that Pezeshkian had told Sir Kier that Western countries’ support for Israel had encouraged it to “continue atrocities” and threatened peace and security.

“Pezeshkian stated that from the point of view of the Islamic Republic of Iran, war in any part of the world is not in the interest of any country, emphasizing that a punitive response to an aggressor is a legal right of states and a way to stop crime and aggression,” Irna added.

The Iranian foreign ministry separately rejected the call for restraint from London, Paris and Berlin.

“Such demands are void of political logic, in complete contradiction to the principles and rules of international law, and excessive,” spokesman Nasser Kaanani said.

The Israeli military said on Monday that it was taking Iran’s statements seriously.

“We are prepared at peak readiness in offence and defence, and we will act according to the directives of the government,” spokesman Rear Admiral Daniel Hagari told a briefing.

An Israeli government spokesman meanwhile warned Iran and its allies that Israel would “exact a heavy price for any aggression against us from any arena”.

US National Security Council spokesman John Kirby told reporters: “We share the same concerns and expectations that our Israeli counterparts have with respect to potential timing here. [It] could be this week.”

“It is difficult to ascertain at this particular time if there is an attack by Iran and or its proxies, what that could look like, but we have to be prepared,” he added.

Defense Secretary Lloyd Austin has dispatched a second aircraft carrier strike group as well as a ballistic missile submarine to the Middle East to reinforce what the Pentagon said was the “United States’ commitment to taking every possible step to defend Israel”.

The US believes that a new deal for a ceasefire in Gaza and the release of Israeli hostages would be the best way to calm tensions in the region, and has called for talks to resume on Thursday.

Israel has said it will send a team of negotiators to finalise a deal, while Hamas has indicated an agreement in principle to participate despite the killing of its leader.

Hamas said on Sunday that any deal must be based on where talks were a month and a half ago, rather than any new rounds of negotiations.

Israel launched a military campaign in Gaza to destroy Hamas in response to an unprecedented attack on southern Israel on 7 October, during which about 1,200 people were killed and 251 were taken hostage.

More than 39,920 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.

Hundreds of people have also been killed in the almost daily exchanges of fire between Hezbollah and the Israeli military across the Israel-Lebanon border since the day after the start of the conflict.