United Nations Secretary General Antonio Guterres on Thursday urged an immediate halt to "all hostile acts" in the Middle East to avoid "a new conflagration" in the region.
The call followed an overt clash between Israel and Iran on Syrian soils, when Israeli forces bombed Iranian targets inside Syria after Iranian-backed militias fired rockets at the Golan Heights.
Israel has called on the U.N. Security Council and Guterres to condemn Iran's attack.
The Security Council, deeply divided over Syria, is highly unlikely to issue a statement and as of Friday morning no council member has asked for a meeting.
The European Union called the Iranian strike against Israel "extremely worrying" and said Israel had the right to defend itself.
It also called on all regional actors to show restraint and avoid any escalation.
"Reports about last night's Iranian attacks against Israeli army posts from inside Syria, to which Israel responded by striking against Iranian targets in Syria, are extremely worrying," said a spokeswoman for the bloc's foreign policy chief, Federica Mogherini.
British Prime Minister Theresa May spoke to her Israeli counterpart Benjamin Netanyahu on Thursday and expressed British support for Israel's right to defend itself against Iranian aggression.
"The prime minister condemned the Iranian rocket attacks against Israeli forces, and said we strongly support Israel's right to defend itself against Iranian aggression," May's office said in a statement.
Netanyahu said Israel's airstrikes were appropriate because Iran had "crossed a red line."
The British statement said May and Netanyahu "agreed it was vital for the international community to continue working together to counter Iran's destabilizing regional activity, and for Russia to use its influence in Syria to prevent further Iranian attacks."
The British statement added that 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."
France and Germany on Thursday urged Israel and Iran to exercise restraint and avoid further escalation of hostilities in the Middle East.
German Chancellor Angela Merkel and French President Emmanuel Macron discussed the Iranian rocket attacks and Israel's response in Aachen, western Germany, and called for prudence and de-escalation.
"The escalations of the past few hours show us that it is truly about war and peace. And I can only call on all sides to exercise restraint here," Merkel said during a ceremony awarding Macron the Charlemagne Prize for strengthening EU integration.
Expectations of a flare-up in the Middle East were stoked by President Donald Trump's announcement on Tuesday that he was withdrawing the United States from the 2015 nuclear deal between Iran and world powers.
The Middle East is becoming very dangerous, 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.
"It is clear that last night's incidents are part of a new context in the Middle East, where what we feared happening is becoming reality: the Syrian and Iranian issues are becoming intertwined," Le Drian told BFM TV.
In her speech in Aachen, Merkel urged the European Union to strengthen its foreign and defense policy, arguing that Europe could no longer fully rely on the United States to protect it.
"Let's face it, Europe is still in its infancy with regard to the common foreign policy," she said. "And it will be existentially necessary to make progress here because the nature of conflicts has completely changed since the end of the Cold War."
Pointing to the civil war in Syria, Merkel said that many of the global conflicts today were flaring on the doorstep of Europe.
"And it is no longer the case that the United States of America will simply protect us. Instead, Europe has to take its destiny into its own hands. That is the task for the future."
Macron echoed the call to flesh out Europe's common foreign and defense policy.
"We made the choice to build peace in the Middle East. Other powers ... haven't kept their word," Macron said, without naming a country directly. "We must succeed in building our own sovereignty, which in this region, will be the guarantor of stability."
Iran, for its part, said Thursday that it does not want "new tensions" in the Middle East.
"Iran has always sought to reduce tensions in the region, trying to strengthen security and stability," President Hassan Rouhani told Merkel, according to a statement on the website of Iran's presidency.
