Japan has condemned the hijacking of a Japanese-operated, British-owned cargo ship in the Red Sea by Iran-backed Houthi rebels.

The Yemeni militia claimed the vessel was Israeli, and a spokesman said the seizure was only the beginning of a "battle at sea".

Israel said the ship was not Israeli and a Japanese government spokesperson said it was operated by Nippon Yusen.

Japan's chief cabinet secretary said it was working towards the ship's release.

Israeli Prime Minister Benjamin Netanyahu blamed the Houthi's backer, Iran, for the hijacking.

Mr Netanyahu said neither the vessel nor the crew were Israeli and called it an "Iranian attack on an international ship". Iran has denied involvement.

Those on board are believed to include Bulgarian, Mexican, Filipino and Ukrainian nationals.

Galaxy Leader is owned by Galaxy Maritime Ltd, which is registered in the Isle of Man. It is owned by Ray Car Carriers, which is co-owned by Israeli businessman Abraham Ungar, according to documents from the Isle of Man Government's Companies registry.

In a statement quoted by Reuters news agency, Galaxy Maritime Ltd said the ship was "illegally boarded by military personnel via a helicopter" on Sunday, and was now being held at the port of Hodeidah in Yemen.

Unverified video footage released by the Houthis on Monday and aired on the group's TV channel, Al Masirah, showed armed men descending from a helicopter onto the ship.

Mr Ungar told The Associated Press news agency he was aware of the incident but could not comment on it.

"The government of Japan absolutely condemns such an act," said Hirokazu Matsuno, Japan's chief cabinet secretary said on Monday, adding there were no Japanese nationals among the crew.

He said ministries and agencies were working with the relevant countries for the early release of the vessel and its crew.

"We are also urging related countries such as Saudi Arabia, Oman and Iran to strongly urge the Houthis to release the ships and sailors as soon as possible."

Matthew Miller, spokesman for the US state department, called the Houthi's seizure of the ship "a flagrant violation of international law" and demanded the "immediate release of the ship and its crew".

Mohammed Abdulsalam, a spokesman for Yemen's Houthi rebels, said on X, formerly Twitter, the group's seizure of the vessel was only "the start" of its fighters waging "battle at sea".

Houthi's military spokesman, Yahya al-Sarea, claimed the ship was Israeli and had been taken to a port in Yemen.

The group had earlier threatened to target any Israeli ship within their reach in response to Israel's retaliatory military action in the Gaza Strip following the 7 October attack by Hamas militants.

More than 1,200 people were killed and more than 240 taken hostage during the surprise Hamas attack on the south of the country, according to the Israeli government.

In retaliation, it launched a massive military operation to try and eliminate Hamas - involving air and artillery strikes as well as ground troops - with the aim of eliminating Hamas.

According to the Hamas-run health ministry, the death toll in Gaza since then has reached 13,300. More than 2,000 more are feared to be buried under rubble.

The Houthis have fired several missiles and drones towards Israel just after Israel launched its retaliatory operation.

The US said at the time that all the missiles and drones were intercepted by its warship in the Red Sea.

The Israel Defense Forces (IDF) described the attack on the ship as a "very grave incident of global consequence".

The IDF said the vessel was on its way from Turkey to India when it was seized in the southern Red Sea near Yemen.

Iranian Foreign Minister Hossein Amir-Abdollahian has recently said that what he called resistance groups allied to Tehran were "cleverly adjusting pressure" on Israel and its supporters.

Earlier this month, the Houthis shot down a US military drone off Yemen's coast, American officials said.

The Houthis have been locked in a prolonged civil war with Yemen's official government - backed by Saudi Arabia - since 2014.

Additional reporting by Shruti Menon