"The United Kingdom condemns in the strongest terms the Iranian rocket attacks against Israeli forces", said UK Foreign Secretary Boris Johnson. Israel intercepted some of the Iranian missiles with the aid of the Iron Dome air defense systems while others fell short of striking the targets.
Russian Federation - which is alone in having close relations with both Iran and Israel - has sought to position itself as a mediator to prevent further escalation. "Strikes from Israel all the way to Iran or vice versa seem less likely, although possible if the local conflict becomes more intense".
Hours later, Israel responded.
Israel Defense Forces also deployed missile defense batteries in northern Israel, stating "there is high preparedness of IDF troops for an attack". "It's a direct war and that's what makes it particularly risky", said Martin Indyk, a former USA ambassador to Israel.
"This is what we have done and this is what we will continue to do", Netanyahu said in the statement.
A series of strikes over the last few months - all blamed on Israel - have struck Iranian assets in Syria and killed Iranian forces there. It said half the missiles were shot down.
Iran and Israel are enemies but have never fought a direct war.
The scope of the attacks - which Israel called its largest in Syria since the 1973 Mideast war - raised the specter of a full-fledged war between Iran and Israel in Syria, a conflict that could potentially drag the militant Hezbollah and Lebanon into the mix with devastating effects, although both sides appeared to signal they wanted the confrontation to remain contained, at least for now. Israel's current defense minister said it took out most of Iran's infrastructure in Syria. Thousands of militiamen armed, trained and financed by Iran have also been battling rebel forces alongside Syrian soldiers, reports say.
In the end, the US, UK, and France all condemned Iran for its missile attack on Israel without mentioning Israeli incursions into Syria to strike Iranians.
Tensions have been rising in the region since President Donald Trump decided two days ago to quit the Iranian nuclear agreement and impose broad sanctions.
The Israeli military didn't confirm the strike; it has a policy against commenting on Syrian airstrikes.
The Middle East was becoming very unsafe, said French Foreign Minister Jean-Yves Le Drian, adding that there was no "Plan B" in response to Trump's move and that France wanted to keep the accord alive even without Washington on board.
Israel said it attacked overnight after Iran's Quds Force, an elite unit of the Revolutionary Guards that's backing Syrian President Bashar al-Assad, targeted Israeli army positions with 20 rockets.
There was no immediate word on Iranian casualties. Israel reported none on its side.
According to the United Nations official, the secretary-general "followed with utmost concern" reports of missile launches from Syria targeting Israeli positions and retaliatory strikes by the Israel Defense Forces.
Information for this article was contributed by Loveday Morris, Ruth Eglash, Louisa Loveluck, Suzan Haidamous, Erin Cunningham, Brian Murphy and John Wagner of The Washington Post; and by Zeina Karam, Aron Heller, Sarah El Deeb, Albert Aji, Vladimir Isachenkov and Ian Deitch of The Associated Press.