Campaigners on the Greek island of Crete launched a seaborne protest on Friday against the destruction of Syrian chemical agents in the Mediterranean, the state-run ANA agency reported.
Some 36 people including local mayors, labour unionists and a leftist MP sailed from the port of Hania aboard three sailboats.
The campaigners plan to reach an area southwest of Crete where the breakdown of Syrian chemical agents is being carried out aboard a US military ship. The US ship's exact location is secret.
"We are on our way to send the message that we want a clean Mediterranean Sea, without chemicals," municipal workers representative Athena Giannoulaki told ANA.
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Hundreds of tonnes of chemical agents were handed over by Syria as part of an international agreement to avoid Western air strikes after a chemical attack in the country caused international outrage.
A US naval ship fitted with hydrolysis equipment, which helps break down lethal chemicals into a sludge, started the job of neutralising the arsenal in international waters last week.
Although the byproducts of the process will be disposed of on land in Finland and Germany, protesters in Greece object to the work being done at sea, fearing the risk of an environmental accident.
"We say 'no' to this environmental crime," said Michalis Kritsotakis, a lawmaker with the radical leftist Syriza party.
NGOs and environmental groups have questioned the safety of the operation and the lack of information being provided to nearby coastal communities.