Yemen's Houthis rebels said on Sunday that they had seized an Israeli ship in the southern Red Sea and taken it to a Yemeni port.
"We are treating the ship's crew in accordance with Islamic principles and values," a spokesperson of the group's military said in a statement.
Earlier, Israel had described the incident as an "Iranian act of terrorism".
"There were no Israelis on the ship," Israeli Prime Minister Benjamin Netanyahu's office said.
"This is another Iranian act of terrorism that represents an escalation in Iran's belligerence against the citizens of the free world, with concomitant international ramifications vis-a -vis the security of global shipping routes."
A US Defense official said "we're aware of the situation and are closely monitoring it".
The Houthis, an ally of Tehran, have been launching long-range missile and drone salvoes at Israel in solidarity with the Palestinian Hamas militants it has been battling in the Gaza Strip since Oct 7.
Last week, the Houthi leader said his forces would make further attacks on Israel and they could target Israeli ships in the Red Sea and the Bab al-Mandeb Strait.