The UK and US believe Iran was behind a tanker attack that killed two people, and have vowed to respond, calling it a violation of international law.
The MV Mercer Street, operated by an Israeli-owned firm, was attacked off Oman.
A British national and a Romanian citizen were killed.
The statements came after Israel’s Prime Minister Naftali Bennett said there was “evidence” that its longstanding foe Iran was responsible.
The attack on the MV Mercer Street appears to be the latest escalation in an undeclared “shadow war” between Israel and Iran.
Since March there have been several attacks on both Israeli and Iranian-operated vessels, which are seen as tit-for-tat incidents. Casualties are considered rare.
Iran has also accused Israel of targeting its nuclear sites and scientists.
US Secretary of State Antony Blinken said Washington was also “confident that Iran conducted this”, and that an “appropriate response” would follow.
Israel’s Prime Minister said it expected the international community to make clear to Iran that it had made a serious mistake.