This handout photo made available on Saturday by Jan Verhoog shows the Stena Impero, a British-flagged tanker, off the coast of Europoort in Rotterdam. AFP

India said on Saturday it is in touch with Tehran for the release of the captured sailors.

Iran on Friday seized the British-flagged Stena Impero, which has Indians, Russians, Latvians and Filipinos working as crew.

Ministry of External Affairs spokesperson Raveesh Kumar said that further details of the incident are being ascertained. "Our Mission is in touch with the Government of Iran to secure the early release and repatriation of Indian nationals."

News agency IRNA quoted Allahmorad Afifipour, Director General of Ports and Maritime Affairs of Hormuzgan province, as saying: "There are 18 Indian and five crew members from Russia, Philippines, Latvia and other countries on board of Stena Impero. The captain is Indian, but the tanker is UK-flagged."

"Stena Impero crashed into a fishing vessel," he said adding that the captain of the vessel tried to make contact with the UK tanker, but there was no signal.

Stena Bulk, the shipping company that owns the vessel, said in a statement, that the tanker was "approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters."

"We are presently unable to contact the vessel which is now heading north towards Iran," it added.

Stena Bulk said, "there have been no reported injuries and their safety is of primary concern to both owners and managers."

The Iranian private Tasnim news agency said that the British-owned Mesdar was cleared to continue its course after having received a warning from the authorities over safety and environmental issues.

British Foreign Secretary Jeremy Hunt termed Iran's action as "unacceptable."

"We're not looking at military options, we're looking at a diplomatic way to resolve the situation, but we are very clear that it must be resolved," Hunt later told Sky News, warning that if the situation is not resolved quickly "there will be serious consequences."

US President Donald Trump said on Friday that Iran is "nothing but trouble" and that "we heard one, we heard two," tankers were seized.

"Iran is showing their colours. Iran is in big trouble right now. Their economy is crashing, it's coming to a crash ... It's very easy to straighten out or it's very easy for us to make it worse," he told reporters.

Late on Friday, US Central Command (CENTCOM) said that Washington had intensified air patrols over the Strait of Hormuz. CENTCOM spokesman Lt. Col. Earl Brown said that US Naval Forces Central Command had been "in contact with US ships operating in the area to ensure their safety."