NEW DELHI: India said Saturday it was in touch with Tehran to secure the release of 18 of its nationals serving on a British-flagged tanker seized by Iran in the Strait of Hormuz.

The Philippines also said it would ask Iran to free a Filipino crew member on the Swedish-owned Stena Impero which was seized on Friday, as tensions mount in a key waterway for the world's oil supplies.

Raveesh Kumar, spokesman for India's foreign ministry, told AFP that 18 of its nationals were on the ship and said New Delhi was "in touch with the government of Iran to secure (their) early release and repatriation".

The tanker was impounded off Bandar Abbas port for breaking "international maritime rules" after colliding with a fishing boat, Iranian authorities said.

The Philippine foreign department said a Filipino, three Russians and a Latvian were also among the ship's crew.

"(Philippine) Ambassador to Iran Fred Santos is contacting Iranian authorities to seek assurance that the Filipino seafarer is safe and will be released soon," it said, adding the unidentified crew member's family has been notified.

The recruitment agency that supplied the Filipino crew member told Manila there were no reported injuries as the vessel headed for the Iranian coast on Friday, the department added.

Iranian authorities said the tanker has anchored off Bandar Abbas with all its 23 crew aboard.

Britain said a second ship had also been seized in the Persian Gulf -- the Liberian-flagged Mesdar.

The Mesdar's British owner said the vessel had been temporarily boarded by armed personnel, but was free to leave and that all crew were "safe and well".

Tensions in the Gulf have soared in recent weeks, with US President Donald Trump in June calling off air strikes against Iran at the last minute after Tehran downed a US drone, and blaming the country for a series of tanker attacks.

Washington has been ratcheting up sanctions against Tehran after the US unilaterally withdrew from a 2015 deal under which Iran agreed to limit its sensitive nuclear development activities in return for the lifting of crippling economic sanctions. —AFP