BRUSSELS: The EU expressed its deep concern on Saturday over the seizure by Iran of a British-flagged tanker in the Strait of Hormuz, saying it brought risks of deepening tensions.

The seizure of two ships by Iranian authorities "is of deep concern"m said a statement by the EU's foreign affairs office, which represents the bloc's 28 member states.

"In an already tense situation, this development brings risks of further escalation and undermines ongoing work to find a way to resolve current tensions," the statement said.

"We urge the immediate release of the remaining ship and its crew, and call for restraint to avoid further tensions," it said, adding that "freedom of navigation must be respected at all times".

The EU's plea came after bloc powers Germany and France condemned the taking of the Stena Impero and the seizing earlier this week of a smaller Panamanian-flagged tanker.

Berlin and Paris both underlined their solidarity with Britain.

Britain, Germany and France were the lead European powers that negotiated with Iran to curb its nuclear programme in a 2015 deal in return for the lifting of sanctions.

President Donald Trump has pulled the US out of the agreement and imposed sanctions to block Iran exporting its oil, much of which transits through the Strait of Hormuz.

Up to now, Britain, Germany and France had sought to keep the deal with Iran alive by setting up a trade mechanism not subject to the US sanctions, but rising military tensions in the Gulf have put that at risk