CNN – An oil spill from a stranded tanker off the coast of Oman now covers an estimated 500 square miles (1,300 square kilometers), the environmental organization Greenpeace told CNN, prompting fears that a major ecological disaster could be unfolding in the Arabian Sea.

The spill has spread to mainland Oman, roughly 120 miles (200km) from the tanker, according to Omani authorities.

Greenpeace campaigner Hanen Keskes said their analysis of satellite images showed fragmented spots, meaning the spill is in multiple areas rather than one continuous mass.