Four Central European countries say they refuse to accept the European Union's plan for member nations to share the burden of hosting a surge of migrants seeking asylum.

The EU's 28 members are at odds over a plan to require countries to take set numbers of refugees arriving in Italy and Greece.

Slovakia, the Czech Republic, Hungary and Poland form a grouping known as V4 that vocally opposes the proposed system of dividing up migrants. They said in a statement Tuesday they consider the plan "unacceptable."

They say they are ready to show their solidarity with Italy and Greece on the migrant situation, but only on a voluntary basis.

Slovak Prime Minister Robert Fico also said Tuesday his government will consider a referendum on the plan if it is pushed through.