Myanmar sailors, together with Ethiopian, Indonesian, and Philippines crew, are being held hostage in a Yemeni port as international powers express concern.

The Saudi-led coalition fighting alongside government forces accused the Iran-backed Huthi rebels of militarising Red Sea ports and threatened to attack them, after the insurgents seized a United Arab Emirates-flagged ship last week with the crew onboard.

"UNMHA reminds the parties that Hodeida ports are a crucial lifeline for millions of Yemeni people," it said in a statement.

The coalition says the seized vessel, the Rwabee, was carrying medical supplies but the Huthis insist it was a military ship.

India on Tuesday appealed for the release of seven Indian nationals who were on board as part of an 11-strong crew, along with others from Myanmar, Ethiopia, Indonesia, and the Philippines.

"The Government of India is making all efforts to secure their early release," said external affairs spokesperson Shri Arindam Bagchi.

"We urge the Huthis to ensure the safety and wellbeing of the crew members, and release them immediately."

The hijacking on January 3 raised fears that the conflict could spill over into the Red Sea, a vital route for Gulf oil and cargo shipments.

It could also have severe consequences for Yemen, which the UN has said is facing the world's worst humanitarian crisis, if it draws attacks on Hodeida.

"UNMHA has requested as part of its mandate to undertake an inspection," the UN statement said, adding that protecting the ports was "in the interest of the Yemeni people".

AFP/Mizzima