US Secretary of State Antony Blinken Monday condemned the "unjustified seizure" of two Greek-flagged vessels by Iran's Revolutionary Guard last week, the State Department said.

Iranian forces seized two Greek tankers in the Gulf on Friday, shortly after Tehran warned it would take punitive action against Athens over the confiscation of Iranian oil by the United States from a tanker held off the Greek coast.

"Iran's continued harassment of vessels and interference with navigational rights and freedoms are a threat to maritime security and the global economy," Blinken said in the statement.

Blinken made the comments in a telephone call with Greek Foreign Minister Nikos Dendias, the department said.

The US and Greek diplomats called on Iran to immediately release the seized vessels, their cargoes, and their crews. Blinken said the United States stands with its NATO ally "in the face of this unjustified seizure."

Iran's state maritime body said on Saturday the crew of the two Greek tankers not been detained, and were in good health and being cared for onboard their vessels.

Greek authorities last month impounded the Iranian-flagged Pegas off Greece due to European Union sanctions. The United States later confiscated the Iranian oil cargo held onboard, Reuters reported on Thursday.

The Pegas and its Russian crew were later released, but the seizure inflamed tensions amid stalled nuclear talks between Iran and the West.