A preliminary investigation into a mushrooming oil spill in waters near Trinidad and Tobago has found that an overturned and abandoned barge blamed for the disaster was being tugged to nearby Guyana.

Officials in the eastern Caribbean island nation are trying to determine the owner of the vessel after last week's spill coated beaches along Tobago's southern coast and forced at least two schools to close over health concerns. 

 Prime Minister Keith Rowley said last week that the country was grappling with a national emergency. 

Trinidad and Tobago Coast Guard, with help from regional agencies and satellite images, determined that the barge and a tug boat were traveling from Panama to the South American nation of Guyana, the National Security Ministry said Wednesday. 

Foreign maritime security investigators also are helping with the ongoing probe, officials said.

Officials have said it was not clear if anybody was aboard the barge when it overturned and apparently began to sink off Tobago's coast. They are still searching for the tug boat and its owner. The mystery ship made no emergency calls, with no sign of crew and no clear indication of ownership.

The spill has angered many residents of the twin-island nation.

Farley Augustine, chief secretary of Tobago's House of Assembly, demanded that the owner of the barge step forward and pay for the cleanup.

"We have a lot of questions, and now is the best time to have those questions answered," he told reporters on Wednesday.

"We need to know the quantity and the material you were transporting, so we know what we have been dealing with, what we have been walking in, what we have been swimming in, what we have been trying to clean up from our shores," Augustine said.

National Security Minister Fitzgerald Hinds said the investigation is continuing. "We look forward to a swift and successful resolution," he said.

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• Oil Spill
• Caribbean