An Israeli soldier stands next to Merkava Mark IV tanks in a deployment area near the Syrian border in the Israel-annexed Golan Heights

The chief of the UN has called for an immediate halt to “all hostile acts” in the Middle East, a day after Israeli forces bombed Iranian military targets inside Syria.

Antonio Guterres, the UN secretary-general, asked for the halt to avoid “a new conflagration” in the region following the most extensive military exchange between Israel and Iran.

Iranian senior cleric Ayatollah Ahmad Khatami said during Friday prayers that Western pressure will backfire, threatening that Israel will pay the price.

"The holy system of Islamic Republic will step up its missile capabilities day by day so that Israel, this occupying regime, will become sleepless and the nightmare will constantly haunt it that if it does anything foolish, we will raze Tel Aviv and Haifa to the ground," the hardline cleric said. The worshippers chanted: "Death to America," and "Death to Israel".

Israel said the strikes were retaliation for an Iranian rocket barrage on its positions in the occupied Golan Heights. It was the most serious military confrontation between the two bitter rivals to date and risks direct clashes which could swiftly escalate.

It comes as Hamas' leader in the Gaza Strip hinted at the possibility thousands of Palestinians could breach the border fence with Israel during mass protests this week.

Israel attack Iran targets in Syria: overnight airstrike in pictures Show all 10 1 /10 Israel attack Iran targets in Syria: overnight airstrike in pictures Israel attack Iran targets in Syria: overnight airstrike in pictures Missiles rise into the sky as Israeli missiles hit air defense position and other military bases, in Damascus Syrian Central Military Media, via AP Israel attack Iran targets in Syria: overnight airstrike in pictures Missile fire is seen from Damascus Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures An Israeli flag is seen placed on Mount Bental in the Israeli-annexed Golan Heights. Israel's army said today it had carried out widespread raids against Iranian targets in Syria overnight after rocket fire towards its forces it blamed on Iran, marking a sharp escalation between the two enemies. Israel carried out the raids after it said around 20 rockets, either Fajr or Grad type, were fired from Syria at its forces in the occupied Golan Heights at around midnight. AFP/Getty Israel attack Iran targets in Syria: overnight airstrike in pictures The Israeli military on Thursday said it attacked "dozens" of Iranian targets in neighboring Syria in response to an Iranian rocket barrage on Israeli positions in the Golan Heights AP Israel attack Iran targets in Syria: overnight airstrike in pictures Israeli artillery deployed missiles toward Syrian military targets, on the Golan Heights EPA Israel attack Iran targets in Syria: overnight airstrike in pictures Missile fire is seen over Daraa Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures Air defence systems intercepting Israeli missiles over Syrian airspace AFP/SANA Israel attack Iran targets in Syria: overnight airstrike in pictures Israeli soldiers walk among armored vehicles in the Israeli-occupied Golan Heights Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures Syrian air defense missiles are seen in the sky over the capital Damascus EPA Israel attack Iran targets in Syria: overnight airstrike in pictures Air defence systems intercepting Israeli missiles over Syrian airspace. Israeli missile strikes fired at Syria hit military bases, as well as an arms depot and military radar. AFP/SANA

Britain supports Israel’s right to defend itself against Iranian aggression, Theresa May, the prime minister, told her Israeli counterpart, Benjamin Netanyahu.

Israel said it had attacked nearly all of Iran’s military infrastructure in Syria on Thursday after Iranian forces fired rockets at Israeli-held territory for the first time.

The Britain-based Syrian Observatory for Human Rights, which closely monitors the civil war through sources inside Syria, said 23 fighters, including five Syrian soldiers, were killed. It was not immediately clear if any Iranians were among the dead.

The confrontation came two days after Donald Trump announced the United States would withdraw, with Israel’s encouragement, from a 2015 nuclear deal with Iran.

The British statement said Ms May and Mr Netanyahu “agreed it was vital for the international community to continue working together to counter Iran’s destabilising regional activity, and for Russia to use its influence in Syria to prevent further Iranian attacks”.

The statement added that Ms May had “reiterated our position on the Iran nuclear deal, noting that we and our European partners remain firmly committed to ensuring the deal is upheld, as the best way of preventing Iran from developing a nuclear weapon”.

The White House swiftly condemned Iran's "provocative rocket attacks from Syria against Israeli citizens" and expressed strong support for "Israel's right to act in self-defence," while Russia said the Israeli strikes marked a dangerous escalation and urged both Israel and Iran to avoid provoking each other.

In a statement, the White House press secretary, Sarah Huckabee Sanders, said "the Iranian regime's deployment into Syria of offensive rocket and missile systems aimed at Israel is an unacceptable and highly dangerous development for the entire Middle East."