PORT OF SPAIN, Dec. 24 -- One of the five oil spills that happened along Trinidad and Tobago's southwestern coast this month has been classified as sabotage, local media reported Tuesday.

"The valves that were opened could have only been opened using a specialized type of wrench," Energy Minister Kevin Ramnarine told a news conference Monday.

Since Dec. 17, five separate oil spills took place along the southwestern coast of the energy-rich southern Caribbean nation, affecting residents and marine life, and polluting the environment.

Fumes from the leaked oil have caused nausea and headache among residents, with 25 hospitalized. Doctors and ambulances were posted in affected areas to respond to people who may feel sick.

The government has beefed up security at all state-owned energy facilities and formed an advisory committee to oversee the situation.

Four foreign experts, two from Britain and two from the United States, arrived here Monday to assess the impact of the oil spills and lead the clean-up efforts.

There were no clues about what caused the other four oil spills but an independent team will investigate the incident, Ramnarine said.