Green Party leader Mr Trevor Sargent has criticised the Government for not doing enough to ensure that a shipment of weapons grade plutonium does not enter Irish waters.
Two British-registered ships, owned by British Nuclear Fuels, are carrying 140 kilogrammes of surplus plutonium oxide from the United States to Cherbourg in France.
They are believed to be passing within 150 miles of the Irish coast on their journey.
Mr Sargent warned the Government that "the Irish people will not be fobbed off by diplomatic statements that everything possible is being done to protect people and the environment from the dangers of nuclear pollution".
He added that the nuclear waste shipments from the United States to Europe must be discontinued as they are a deadly hazard and herald a whole new generation of nuclear reactors using MOX fuel made from weapons grade plutonium.
"Assurances given by the Government that the ships do not plan to enter Irish waters are not enough. The Government must send naval vessels to the limits of Irish waters to make sure that this deadly cargo does not enter Irish waters," Mr Sargent said.
He added: "Following the International Atomic Energy Agency line, the Green Party advocates treating plutonium as nuclear waste through immobilisation, which is safer, cheaper and a more secure method rather than carrying on with proliferation risks by using it in "civil nuclear industry."
Mr Sargent warned that "the potential dangers this nuclear flotilla poses to Ireland should not be underestimated. 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".
The Green Party is also calling on the Government to challenge the EU Euratom Treaty, which is a nuclear industry-run policy that it says puts business and profits for the industry before the health and safety of people.
Sinn Féin MEP for Dublin Ms Mary Lou McDonald also criticised the government today, saying that '"Irish waters have become a nuclear corridor effectively putting the lives of millions of people at risk".
She added: "It is only a few weeks since the European Commission decision to initiate legal proceedings in the European Court of Justice against the British Government, for their failure to comply with strict EU inspection rules on nuclear waste at their Sellafield plant."
She called upon the Taoiseach and the Minister for the Environment to ensure that any future vogages do not pass through Irish waters.
A spokeswoman for the Department of the Environment told ireland.comlast week it had sought and received assurances that the ships "would not be passing through Irish waters".