The Philippines said Wednesday that Iran has freed all 18 Filipino crew members of an oil tanker that was seized in the Gulf of Oman in January.

Iran's navy had boarded the Greek-owned St. Nikolas, which was carrying 19 crew, off the coast of Oman. The only Greek crew member was released the following week.

Tehran began freeing the Filipino crew in batches at the end of January after a replacement crew was hired from Russia and other countries, Philippine Foreign Undersecretary Eduardo de Vega told AFP.

"They were not hostages... but they were not allowed to leave without replacements," de Vega said of the Filipino crew.

The last of the Filipino crew returned to Manila last week, he added.

The Marshall Islands-flagged ship was carrying 145,000 tonnes of oil from Iraq and heading to Turkey when it was seized. It has been anchored in the vicinity of the Iranian port of Bandar Abbas.

Iran's state media has said the seizure was in retaliation to the "theft" Iranian oil by the United States from the same tanker, at the time named the Suez Rajan.

- Tit-for-tat -

Tehran has responded with tit-for-tat measures in the past after seizures of Iranian oil shipments.

Crippling US sanctions, reimposed following Washington's 2018 withdrawal from a landmark nuclear deal, target Iranian oil and petrochemical sales in a bid to reduce Iran's energy exports.

Manila is still seeking the release of 17 Filipinos taken hostage by Yemen's Iran-backed Huthis in November after the rebels seized their ship in the Red Sea.

In a separate incident, two Filipino crew members were killed and three others injured in a Huthi missile attack on their ship in the Gulf of Aden on March 6.

The Huthis began attacking ships in the Gulf of Aden and the Red Sea last November, a campaign they say is intended to signal solidarity with Palestinians in Gaza.

De Vega said Manila was "encouraged by the developments such as the UN resolution calling on a ceasefire in Gaza".

"Hopefully there will be peace in the Middle East and the Huthis will release them (Filipino seamen)," he said.