Fears of escalation after Israel kills leaders of Hamas and Hezbollah

Iran vowed revenge yesterday after airstrikes killed the Hamas political leader, Ismail Haniyeh, in Tehran and a senior Hezbollah commander in Beirut in the space of 12 hours, dual Israeli assassinations that crushed hopes of an imminent Gaza ceasefire and fuelled fears of a "dangerous escalation" in the region.

- Emma Graham-Harrison, Quique Kierszenbaum and Sufian Taha

Israel did not directly claim the attack on Haniyeh, but there was little doubt among the country's enemies, and its own politicians and analysts, about who was responsible.

Haniyeh was killed by a missile that hit him "directly" in a state guesthouse where he was staying, Khalil al-Hayya, a senior Hamas official, told a news conference in Tehran, quoting witnesses who were with Haniyeh.

He was visiting for the inauguration of Iran's new president, Masoud Pezeshkian, who said after the killing that his country would defend its territorial integrity and honour.

Iran's supreme leader, Ayatollah Ali Khamenei, blamed Israel and said Iran had a "duty" of revenge because Haniyeh was targeted while a guest in the country.

The timing and location of the attacks, targeting high-profile commanders in densely populated capital cities, made them particularly humiliating for Iran and Hezbollah, raising the prospect of a slide towards fullblown regional war as Tehran seeks to re-establish a military deterrent.

Although Hamas has also vowed revenge, after nearly 10 months fighting in Gaza it has little capacity to inflict damage beyond the strip.

Security forces and officials in Israel, Iran and Lebanon mostly agree that all-out conflict would be devastating for all parties, regardless of who emerged victorious.

But in the high-stakes efforts to project power in a regional proxy war, the risk of miscalculation and deadly mistakes is spiralling.

The United Nations secretary general, António Guterres, believes the attacks mark a "dangerous escalation", his spokesperson, Stéphane Dujarric, said in a statement that all parties were urged to work towards de-escalation, adding: "Restraint alone is insufficient at this extremely sensitive time."