An international operation to destroy Syria's chemical weapons stockpile at sea was called a major environmental threat to the Mediterranean this week.

A coalition of marine science experts and environmental non-governmental groups led by the Archipelagos Institute of Marine Conservation in Greece said Tuesday the United Nations-backed plan to neutralize Syria's chemical stockpile while aboard a ship in the Mediterranean Sea was risky and unprecedented.

Under Syria's agreement with the U.N. Security Council, its entire chemical arsenal is to be eliminated by June 30 -- a goal that is becoming increasingly unlikely after Damascus missed a deadline this month to surrender its entire stockpile of chemical weapons.

In a process to be supervised by the Organization for the Prohibition of Chemical Weapons and financially backed by the European Union, a hydrolysis system aboard a U.S. cargo ship sailing in international waters between Crete and Sicily will use heated water mixed with other chemicals to neutralize the lethal agents, producing a sludge similar to industrial toxic waste, the Malta Independent reported.

Anastasia Miliou, research director of the Archipelagos Institute, said the neutralization of chemical weapons at sea is untested and fraught with dangers to the fragile Mediterranean ecosystem and the coastlines of Crete, Malta and Italy.

"The Archipelagos Institute and numerous other experts are highly concerned about the potential hazards of such a complex destructive process," she said. "Not only has this type of procedure never been carried out before, it is also the first time these chemicals will be used to such an extent in the highly unstable marine environment."

The process, she added, also poses threats to marine life "due to the possible dumping of liquid waste produced during the process," she asserted.

"It is contradictory to demand detailed environmental impact assessments and public consultations before authorizing the construction of a simple sewage treatment plant, while carrying out major operations such as dangerous chemical waste treatment, under unclear procedures, with media as the only source of information for national authorities, is considered adequate," added Evangelos Gidarakos of the University of Crete.

The statement was signed by institutions, NGOs, citizens' movements and environmental institutes from Greece, Italy, Israel, Malta, Cyprus, Slovenia, Spain and Belgium, as well as university professors from the Netherlands, Britain, Spain, Norway, Sweden, Italy, Greece, Germany and Austria.

Time is of the essence, they warned, noting media reports that two ships loaded with chemical weapons are already en route to the Mediterranean site, with one in Cyprus and another in Italy.

The coalition called on Greek, Italian and European authorities to call off the operation until a suitable land-based alternative can be found or the sea-based operation is put under the supervision of "impartial scientific experts" to ensure the safety of the marine environment.

Greek Foreign Minister Evangelos Venizelos, however, said this month the sea-based disposal poses no environmental threat, the Malta newspaper reported.

"Our concerted diplomatic efforts ... have given many institutional and scientific guarantees that there is truly no threat to the marine environment," he said. "NGOs, with which I am in contact, are in close cooperation with the Organization for the Prohibition of Chemical Weapons so that we can be certain that there will be no harm to the Mediterranean environment."