The United Nations, Russia, France, Germany and Britain have urged Israel and Iran to avoid any further escalation after Israel carried out air raids against what it said were Iranian targets in Syria.
Iran made no comment about the rocket fire.
UN Secretary-General Antonio Guterres appealed for an “immediate halt to all hostile acts” in a statement.
He urged the Security Council to remain actively aware of the situation and “shoulder its responsibilities” under the UN Charter.
Russia’s Foreign Minister Sergey Lavrov was also quick to call for restraint. He said the Israeli raids were “very alarming development” and called on both Israel and Iran to avoid provoking each other.
All issues “should be solved through dialogue”, he added.
Israel has long warned it will not accept Iran entrenching itself militarily in Syria.
In recent years, it has been suspected of carrying out air strikes on installations manned by Syrian, Iranian, and allied Lebanese fighters across Syria.
Israeli Prime Minister Benjamin Netanyahu said on Thursday Iran had “crossed a red line” and the resulting bombardment “was a consequence”.
“Iran has always sought to reduce tensions in the region, trying to strengthen security and stability,” Rouhani told Merkel in a telephone call, according to a statement on the website of Iran’s presidency.
The White House also condemned Iran’s “provocative attack” in a statement, with press secretary Sarah Huckabee Sanders saying Iran has deployed into Syria “offensive rocket and missile systems aimed at Israel”.
That deployment “is an unacceptable and highly dangerous development for the entire Middle East”, she said.
Merkel and French President Emmanuel Macron, following a meeting in Aachen, Germany on Thursday, called for “level-headedness and de-escalation in the region”.
British Foreign Secretary Boris Johnson said Iran must refrain from “further actions that will only lead to increased instability”, and called on Russia to press the Syrian government to work for a broader political statement.
Meanwhile, in a rare move for an Arab country, Bahrain backed Israel’s right to “defend itself” after the air raids.
Foreign Minister Khalid bin Ahmed Al Khalifa wrote on Twitter that so long as Iran uses its forces and missiles to try and destabilise the region, “it is the right of any country in the region, including Israel, to defend itself by destroying sources of danger.”
Bahrain is a close ally of Saudi Arabia and the two countries, whose foreign policies are often in lockstep, view Iran as the chief threat to the region.
Outside observers see a dangerous game of brinkmanship.
“The rules of the game are worked out by trial and error, by push and shove. The pushing and shoving has become more intense,” said Heiko Wimmen of the International Crisis Group. “We are getting closer to the brink.”
It was only a matter of time before Iran pushed back, said Wimmen.
“The point will come with these actions where the Iranians will say, ‘We have to push back forcefully, we have to establish deterrence against the Israelis if we want to stay in Syria,'” said Wimmen.
Israel, too, may feel emboldened by US President Donald Trump’s decision to withdraw from the 2015 Iran nuclear deal.
“Israel has been chomping at the bit to take a big bite out of Iran’s forces in Syria,” said Nicholas Heras of the Center for a New American Security.
Netanyahu sees that decision as a “green light to go after Iran in Syria, the consequences be damned”, said Heras.
“The Israelis believe they are facing a nightmare scenario right now where Iran is on the march in Syria with the intention to start a war that will end Israel.”