Operation to tow stricken tanker and avert spill starts in Red Sea - shipping source

(Adds EU naval mission statement)

ATHENS, Sept 14 (Reuters) - The operation has started to tow a Greek-registered oil tanker stranded in the Red Sea after an attack by Houthi militants last month, a shipping source told Reuters on Saturday.

Towing the 900-foot (274.2-metre) MV Sounion to safety is the first step in a risky operation to salvage the vessel that caught fire after it was repeatedly attacked on Aug. 21.

The second step is the transfer of its cargo of about 1 million barrels of crude oil. Saudi Arabia, a key player in the region, will offer its assistance with that project, sources have said.

Any oil spill could be one of the largest from a ship, risking catastrophic environmental damage in an area that is particularly dangerous to enter. An initial effort to salvage the vessel was paused earlier this month due to safety reasons.

At least two tugboats owned by a Greek-based salvage company are involved in the latest towing attempt, sources told Reuters on Thursday.

Aspides, the European Union's naval mission in the Red Sea, said on Saturday that its assets were in the area to protect the vessels involved in the operation. It described the operation as a "complex endeavour".

"Creating a secure environment is necessary for the tugboats to conduct the towing operation," Aspides said in a statement on Facebook.

"The salvage operation of the MV Sounion is essential in order to avert a potential environmental disaster in the region. To achieve this, several public and private actors are working together."

(Reporting by Renee Maltezou; Editing by Louise Heavens)