The Government has dispatched the Coast Guard and the Air Corps to insure that ships carrying weapons-grade plutonium do not pass through Irish territorial waters, although it does not know the ships' location.
The shipment, which is in transit from the US port of Charleston to Cherbourg in France, is believed to have passed within 150 miles of the Irish coast in recent days.
A spokesman from the Department of the Environment said the Government had received assurances from the US and France that the two vessels would remain in international waters.
"The Coast Guard and the Air Corps have been dispatched, but we have no reason to believe that the assurances we have had are false. There isn't any reason to go through Irish waters to get from the US to France."
The Government had not been given the co-ordinates of the ships, he said, and did not know when they would be at their nearest point to Irish shores.
"Normally those sort of details about the route and when the vessels will berth are not given for security reasons."
The leader of the Green Party, Mr Trevor Sargent, welcomed the Government's decision to deploy its forces to monitor the coastline, but he said it was still relying too heavily on diplomatic assurances.
"I'm not happy that the Government seems to see this as an isolated incident. Under the current plans, 34 tonnes of nuclear material is due to be shipped."
The cargo of 134 kg of plutonium oxide taken from the warheads of US missiles will be reprocessed in France into nuclear reactor fuel before being shipped back to the US next year. The radioactive cargo is being transported on ships owned by British Nuclear Fuels.
"Nuclear waste shipments from the US to Europe must be discontinued as they are not only a deadly hazard in themselves but they herald a whole new generation of nuclear reactors using MOX fuel made from weapons grade plutonium," Mr Sargent said.
The potential dangers which the nuclear flotilla posed should not be underestimated, he said.
"Fire on a plutonium shipment would result in a radioactive cloud, hundreds of square kilometres large, in a matter of hours. An accident could lead to plutonium fallout in Ireland."
Meanwhile, the anti-nuclear activists arrested on Sunday after they entered a military exclusion zone near the military facilities at Cherbourg port have been released.
The activists were part of a Greenpeace-organised flotilla, which was awaiting the arrival of the armed nuclear convoy.
The French former Round the World yacht race winner, Eugene Riguidel, Mr Jon Castle from Guernsey and a Swedish protester Ms Pernilla Svenberg, were released at 11 a.m. yesterday after spending the night in a French prison.
The three have been charged with trespassing on a military base and are due to appear in court in November.
