The EU has agreed to expand sanctions on Iranian producers of drones and missiles following Tehran's unprecedented attack on Israel.
"It's very important to do everything to isolate Iran," European Council President Charles Michel said.
The bloc already has multiple sanctions in place against Iran, including for selling drones to Russia for use in its war against Ukraine.
The US has hinted it will impose its own new penalties in the coming days.
The EU's new sanctions were agreed during a summit in Brussels which marked the first meeting between the bloc's 27 leaders since Iran's direct assault on Israel on Saturday, involving more than 300 missiles and drones fired from Iran, Iraq, Syria and Yemen which were mostly downed by Israel and its allies.
Tehran has maintained it was retaliation for a presumed Israeli air strike on its consulate in Syria on 1 April, in which 13 people were killed.
Israel - which appears to have only countered with a diplomatic offensive so far - has not ruled out a response.
But world leaders have continued to urge restraint, in a bid to prevent a wider conflict in the Middle East.
"For us, it is important that this moment is now also used for further de-escalation and that Israel also uses this success to strengthen its position in the whole region and not respond with a massive attack of its own," German Chancellor Olaf Scholz said after Wednesday's meeting.
Israel has called on its allies to sanction Tehran's missile programme and for the Islamic Revolutionary Guard Corps (IRGC) - a major military and political force in Iran - to be designated a terrorist organisation, something the US has done but the EU and UK have not.
The EU already has a wide range of measures in place which target Iran over its human rights abuses, nuclear proliferation activities and military support for Russia.
Speaking about the possibility of further sanctions on Tuesday, US Treasury Secretary Janet Yellen said that "all options to disrupt terrorist financing of Iran continue to be on the table".
She also signalled that Iran's oil exports could be "a possible area" Washington targets.
"Clearly, Iran is continuing to export some oil. There may be more that we could do."
In a later statement, US National Security Advisor Jake Sullivan said that Iran's missile and drone programme as well as the IRGC and the Iranian defence ministry would also be covered.
