The decision by the Tel Aviv municipality to light up city hall with the colours of the Lebanese flag caused controversy,with many on the right describing the gesture as an expression of sympathy with Israel’s enemy.
Prime minister Binyamin Netanyahu's eldest son Yair was one of the first to criticise the act of solidarity following the Beirut explosion.
"It's simply insane. Lebanon is formally an enemy country. By law, it is a criminal offence to fly an enemy ," he said.
Leading journalist Amit Segal, considered close to Mr Netanyahu, commented sarcastically on Twitter: "Peace will arrive when the city square in Beirut is lit up with the Israeli flag."
Tel Aviv mayor Ron Huldai defended the humanitarian gesture.
“Humanity takes precedence over every conflict, and our heart is with the Lebanese people in the aftermath of the terrible disaster that they’ve suffered,” he said.
Israel and Lebanon remain technically in a state of war and as in 2006 Israel and the Iranian-backed Shia Hizbullah, the strongest force in Lebanon, fought a one-month war. Earlier this week Israel's defence minister Benny Gantz ordered the army to bomb Lebanese infrastructure if Hizbullah harmed Israeli soldiers or civilians.
Despite the hostility, Mr Netanyahu offered to provide humanitarian assistance to Lebanon following the blast, noting that he had offered similar aid to Iran when it had suffered natural disasters, because "we have no fight with either the Lebanese people or the Iranian people, only with their governments".
However, critics in Israel and abroad claimed the Israeli offers were merely a public-relations stunt, considering that Hizbullah would reject out of hand any Israeli overtures.
The Israeli proposals for assistance, including an offer to provide medical equipment, were relayed via the United Nations, France and Cyprus. Israel said it would leave the Hebrew writing on the equipment so that people in Lebanon know that the aid came from there.
Another proposal was that foreign nationals injured in the explosion could receive treatment in Israeli hospitals or a field hospital could be established on the border.
Israeli Arab doctors were amongst those pleading for Lebanon to respond positively. Dr Masad Barhoum, director-general of Galilee Medical Centrein Nahariya, just a few kilometres from the Lebanese border, suggested that the injured could be transferred to Israel via the UN Interim Force in Lebanon and then returned the same way, crossing at the Ras al-Naqoura crossing.
Ziv Medical Center in Safed, also close to the border, said it was "experienced and prepared" to take in wounded.
Ziv's director, Dr Salman Zarka, said Israel was ready to help. "It's a shame that people will die for no reason."