"Israel's support remains unchanged", Netanyahu said. "This massacre was a significant escalation in a pattern of chemical weapons use by that very bad regime".
Lebanon's Iran-backed militant group Hezbollah early in the day said that Israel had made a "historic blunder" using all the attack.
They "are responsible for the regional consequences of this adventurist action", it said, condemning a "clear violation of worldwide rules and laws".
Relations between Israel and Syria have been strained recently, with the Israeli military conducting attacks on Syrian territory.
"Syria and Russia are fighting a battle not only against terrorism, but also for protecting worldwide law ... based on respect for state sovereignty and the will of their people", Assad said at a meeting with members of Russia's ruling United Russia Party.
"Israel fully supports (U.S.) President Trump's decision to act against the use of chemical weapons in Syria, and Israel welcomes the joining of British Prime Minister Theresa May and French President Emmanuel Macaron in this action", Netanyahu told his ministers during the weekly cabinet meeting.
Punitive US-led strikes on Syria are justified because of the "murderous actions" carried out by the Damascus government, an Israeli official said Saturday.
He also warned Syrian dictator Bashar al-Assad that he was risking his own regime by using chemical weapons. "This morning, the US, Britain, and France proved that their commitment to the fight against chemical weapons is not limited to statements only", he added.
The three countries had carried out a wave of pre-dawn missile strikes, hitting targets near Damascus and in Homs province, Western officials said.
Early on Saturday, the USA, the United Kingdom and France fired more than 100 missiles from ships and manned aircraft at Syria in response to an alleged chemical attack in the city of Douma, which the countries blamed on Damascus.