Salvagers abandoned an initial effort to tow away a burning oil tanker in the Red Sea targeted by Yemen’s Houthi rebels as it “was not safe to proceed,” a European Union naval mission said Tuesday, leaving the Sounion stranded and its 1 million barrels of oil at risk of spilling.

While a major spill has yet to occur, the incident threatens to become one of the worst yet in the Iranian-backed rebels’ campaign that has disrupted the $1 trillion in goods that pass through the Red Sea each year over the Israel-Hamas war in the Gaza Strip. It also has halted some aid shipments to conflict-ravaged Sudan and Yemen.

“The private companies responsible for the salvage operation have concluded that the conditions were not met to conduct the towing operation and that it was not safe to proceed,” the EU’s Operation Aspides mission said, without elaborating. “Alternative solutions are now being explored by the private companies.”

The EU mission did not respond to questions from The Associated Press about the announcement. The safety issue could be the fire burning aboard the vessel. Satellite images from Planet Labs PBC taken Tuesday afternoon and analyzed by the AP showed the Sounion still ablaze.