Britain said Friday it was sending a second warship to the Gulf and raising the alert level in the region as tensions spike after Iranian gunboats threatened a UK supertanker.
The decision was disclosed as US President Donald Trump stepped up his war of words with the Islamic republic over its nuclear programme and its alleged support for terror groups in the Middle East.
"Iran better be careful," Trump told reporters outside the White House. "They're treading on very dangerous territory. Iran, if you're listening, you better be careful."