The European Union (EU) on Saturday said the seizure of two ships by Iranian authorities in the Strait of Hormuz is "of deep concern."

"In an already tense situation, this development brings risks of further escalation and undermines ongoing work to find a way to resolve current tensions," said a statement from the EU spokesperson for Foreign Affairs and Security Policy.

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