A cargo ship believed to be carrying hundreds of migrants headed toward Italy on Tuesday, after telling Greek authorities it didn't require any assistance following an emergency call made by a passenger.

A passenger on board the Moldovan-flagged Blue Sky M called emergency services in Greece earlier in the day when it was sailing off the coast of the island of Corfu in the Ionian Sea.

Greek authorities scrambled a navy frigate and a helicopter to check on the status of the ship and the nature of the emergency. The ship was believed to be carrying between 400 and 600 migrants.

The passenger's phone call said the ship was about 10 miles off Corfu with a large number of migrants, said Adm. Nikolaos Patrinos, head of the coast guard's security operations. The passenger said that "we are without water, food and blankets."

A coast guard official said the Greek frigate had contacted the cargo ship's captain, who said the ship wasn't in any danger and wasn't requesting any assistance. The ship headed toward Italy.

The official spoke on condition of anonymity because he wasn't authorized to speak on the record.

Tens of thousands of migrants and refugees, most fleeing conflict or poverty in the Middle East, Africa and Asia, attempt to reach the European Union each year, with many making the perilous crossing by sea to Italy or Greece.

On Sunday, Greek passenger ferry Norman Atlantic caught fire in the same area, leading to a massive two-day rescue operation by Italian and Greek coast guard and military officials. At least 11 people died in that incident, while more than 400 were rescued. Authorities are still searching for potential missing passengers from the ferry.

The Greek frigate had been in the area assisting in the Norman Atlantic rescue operation.