Long-understood rules governing balance of deterrence between militant group and Israel have been blown away

• Middle East crisis – latest news updates

Israel’s claimed assassination of Hezbollah’s leader, Sayyed Hassan Nasrallah, in a massive strike on an underground headquarters in Beirut’s southern suburbs marks the most alarming escalation in almost a year of war between the Shia militant organisation and Israel.

Immediately after a bellicose speech by the Israeli prime minister, Benjamin Netanyahu, at the UN general assembly – where he appeared to directly threaten Iran as well as promise to continue “degrading” Hezbollah – the first reports of a major strike began to emerge.

Two confirmed dead and 76 hurt but other reports claim hundreds killed as sources close to Hezbollah say Hassan Nasrallah is alive

• Middle East crisis – latest news updates

Israel has launched its heaviest air attack on Beirut in almost a year of conflict with the Lebanese militant group Hezbollah, levelling a number of buildings in a southern suburb in what Israeli media reported as an attempt to kill Hezbollah’s leader and key Iran ally, Hassan Nasrallah.

Six loud explosions were heard across the Lebanese capital late on Friday afternoon, and multiple vast plumes of smoke were visible from as far as Batroun, a city an hour’s drive away.

Conventional wisdom suggested he would resist triggering full-scale war, but the ground appears to be shifting

Twenty-four years ago, on 26 May 2000, Hezbollah’s general secretary, Hassan Nasrallah, arrived in the small Lebanese town of Bint Jbeil a few kilometres from the Israeli border.

The day before, Israel had withdrawn its forces from southern Lebanon after a years-long occupation in which it was harried by Hezbollah and other groups. Thousands of supporters gathered there under Hezbollah’s yellow banners.

Twin statements by Israeli PM appear to wrongfoot US officials ahead of his speech at UN general assembly

• Middle East crisis – latest news updates

Optimism that a three-week ceasefire could be reached between Hezbollah and Israel appeared to recede as Benjamin Netanyahu issued a pair of contradictory statements on the proposal within hours of each other.

In the latest statement from Netanyahu’s office, issued overnight on Friday, the Israeli prime minister chided reporting on the issue as he confirmed Israel had been consulted regarding a US-led ceasefire proposal.