Nato and the EU have joined the condemnation of the deadly attack on an oil tanker blamed on Iran by world powers.
A British and a Romanian national were killed in the suspected drone attack in the Arabian Sea.
After the UK and US pointed the finger at Tehran, a Nato spokesman said the alliance was concerned by Iran’s “destabilising actions” in the region.
“We join allies in strongly condemning the recent fatal attack on the MV Mercer Street,” the spokesman said.
“Freedom of navigation is vital for all Nato allies, and must be upheld in accordance with international law.”
Welcoming Nato's comments, UK Foreign Secretary Dominic Raab said: "We believe this was a deliberate, targeted attack by Iran – it must end its destabilising actions immediately."
Brussels called for an independent investigation into the attack, which took place off the coast of Oman on Thursday.
“Such acts contrary to the security and freedom of navigation in the region are unacceptable,” European Commission spokeswoman Nabila Massrali said.
“All parties concerned must avoid all actions that could undermine peace and regional stability.”
Iran denied responsibility for the attack against a vessel linked to prominent Israeli billionaire Eyal Ofer.
The Liberian-flagged, Japanese-owned tanker was managed by the Israeli-owned company Zodiac Maritime, whose chairman is Mr Ofer.
The attack happened amid protracted negotiations on a revival of the nuclear deal between Iran and world powers, which the US abandoned in 2018.
US Secretary of State Antony Blinken said last week that the talks could not go on forever but that Washington was prepared to continue.
After the Mercer Street incident, he said Washington would seek a collective response and accused Iran of acting with “tremendous irresponsibility”.
He said it followed a “pattern of attacks and other belligerent behaviour” by Iran.
Israeli Prime Minister Naftali Bennett said his country was capable of responding alone if necessary. He said Israel had shared intelligence with the US, Britain and others tying Iran to the attack.
“Iran already knows the price we exact when someone threatens our security,” he said.
“The Iranians need to understand that it is impossible to sit placidly in Tehran and ignite the entire Middle East from there. That's over."