Russia, Germany and the UK on Thursday urged countries in the Middle East to show restraint and Israel said it was preparing to "meet all its security needs" in a region on edge over an Iranian threat to strike Israel.
The German airline Lufthansa, one of only two Western carriers flying to Tehran, extended a suspension of its flights to the Iranian capital and Russia warned against travel to the Middle East.
Iran has vowed revenge for the April 1 airstrike on its embassy compound in Damascus that killed a top Iranian general and six other military officers, ratcheting up tension in a region already strained by the Gaza war.
Israel has not claimed responsibility for the attack but Iran Supreme Leader Ayatollah Ali Khamenei said on Wednesday it "must be punished and it shall be", saying it was tantamount to an attack on Iranian soil. Iran has signalled to Washington it will respond to Israel's attack in a way that aims to avoid major escalation and it will not act hastily, Iranian sources said.
Yoav Gallant, Israel's Defence Minister, told his US counterpart Lloyd Austin Israel would respond directly to any attack by Iran, Gallant's office said.
Conflict has spread across the Middle East since the eruption of the Gaza war, with Iran-backed groups declaring support for the Palestinians waging attacks from Lebanon, Yemen and Iraq. Tehran has avoided direct confrontation with Israel or the US, while declaring support for its allies.
Germany Foreign Minister Annalena Baerbock called on her Iranian counterpart Hossein Amirabdollahian to urge "maximum restraint" to avoid further escalation.
Russia's foreign ministry told citizens they should not travel to the Middle East, especially to Israel, Lebanon and the Palestinian territories.
"Right now, it's very important for everyone to maintain restraint so as not to lead to a complete destabilisation of the situation in the region, which doesn't exactly shine with stability and predictability," Kremlin spokesman Dmitry Peskov told a news briefing.
'Potential for miscalculation'
UK foreign minister David Cameron said on Thursday he had made clear to Amirabdollahian Iran should not draw the Middle East into a wider conflict.
"I am deeply concerned about the potential for miscalculation leading to further violence," Cameron said on X.
US State Department spokesperson Matthew Miller said Secretary of State Anthony Blinken called counterparts including the Turkish, Chinese and Saudi foreign minister "to make clear that escalation is not in anyone's interest and that countries should urge Iran not to escalate". President Joe Biden said on Wednesday Iran was threatening to launch a "significant attack in Israel", and he had told Israel Prime Minister Benjamin Netanyahu "our commitment to... security against these threats from Iran and its proxies is iron-clad".
Iran is the third-largest oil producer in the OPEC group and prices stayed near six-month highs on Thursday.
Late on Wednesday, an Iranian news agency published an Arabic report on the X platform saying the air space over Tehran had been closed for military drills but then removed the report and denied it had issued such news.
Lufthansa said it would probably not fly to Tehran before April 13. Austrian Airlines said it was still planning to fly on Thursday but was adjusting timings to avoid crew having to disembark for an overnight layover.
Iranian air space is also a key overflight route for Emirates' and Qatar Airways' flights to Europe and North America.
Emirates, Qatar Airways, Turkish Airlines, Aeroflot and Air Arabia, among the airlines that fly to Tehran, did not immediately respond to requests for comment.
