By Jonathan Saul and Mohammed Ghobari

ADEN (Reuters) - Some 200 seafarers aboard more than 15 ships stuck for weeks off Yemen's port of Ras Isa are preparing to offload cargoes and leave thanks to a ceasefire deal between Houthi militia and the U.S., maritime and labour union sources said on Thursday.

Still, threat levels for shipping remained high given the Houthis' confirmation that Israeli-related assets remained open to attack and the attendant risks to broader shipping, maritime officials said. Ships with no connection to Israel had been targeted in the past with no certainty of safe passage.

President Donald Trump announced on Tuesday the U.S. would stop bombing the Iran-aligned Houthis in Yemen as they had agreed to stop targeting U.S. ships in Red Sea waters off the Arabian Peninsula country.

However, the deal does not cover close U.S. ally Israel, the Houthis stated on Wednesday, suggesting its attacks on shipping in professed solidarity with Palestinian militants fighting Israel in Gaza might not come to a complete halt.

A nearly two-month-long U.S. bombing campaign in Yemen dealt heavy damage to the Houthis, with a spillover impact on shipping in the Ras Isa region on the Red Sea, a critical artery for world trade.

Several crew members on ships in the vicinity of U.S. air strikes were injured, and two vessels prevented from sailing away by Houthis, according to the International Transport Workers' Federation (ITF), the biggest seafarers' union.

A Houthi official told Reuters that following the agreement with Washington, ships should now be able to enter Ras Isa, discharge cargoes and depart without issues.

At least one of the vessels - mainly tankers carrying fuel supplies including liquefied petroleum gas - was moving into the port to begin discharging cargo on Thursday, according to ship tracking data on the MarineTraffic platform.

NO GUARANTEE OF SAFE PASSAGE

While the risk of collateral damage from airstrikes has abated, seafarers remained concerned about Israeli attacks on Houthi targets in the region.

In response to Houthi drones launched at Israel over the past week, Israeli warplanes hit the major Yemeni Red Sea port of Hodeidah, causing some damage, shipping sources said.

Some of the vessels stuck have been waiting for weeks to discharge in Ras Isa and were urgently seeking to leave the area, the captain of one of the vessels, who declined to be identified due to the sensitive situation, told Reuters.

"The ITF is working urgently to support these crews, but they need more than words; they need safe passage home," ITF General Secretary Stephen Cotton said.

The Houthis have carried out more than 100 attacks on ships plying the Red Sea since November 2023, saying they were acting in support of Palestinians in Israeli-besieged Gaza. They have sunk two vessels, seized one and killed at least four seafarers. There have been no known attacks since January this year.

Many shipping companies have halted voyages through the Red Sea amid uncertainty over whether the ceasefire deal will stick.

"We do not send ships in until we are sure that the people on board are safe," Lasse Kristoffersen, CEO with shipping company Wallenius Wilhelmsen, told Reuters on Thursday.

"We have no information at this time to suggest that."

(Reporting by Jonathan Saul in London and Mohammad Ghobari in Aden, Marie Mannes in Stockholm; editing by Mark Heinrich)