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.

Video of the strikes suggested they were carried out with ground-penetrating munitions known as bunker busters. In some footage, a vertical jet of flame was visible as a bomb appeared to explode beneath the ground.

The strikes came shortly after the Israeli prime minister, Benjamin Netanyahu, told the UN general assembly in a bellicose speech marked by the walkout of dozens of diplomats that Israel’s campaign against Hezbollah would continue despite international efforts to secure a three-week ceasefire.

Israeli media reported that Nasrallah was the target and that the military was checking whether he had been hit. Sources close to Hezbollah told Reuters he was alive.