Serbia has denied entry to a train from Bulgaria after discovering a carriage laden with radioactive material, the customs service said Monday.

`Serbian Customs found radioactivity 3,000 times over permitted levels inside one of the carriages of the train and 300 times on the (outer) surface of the carriage,` it said in a statement sent to AFP.

The train, which was stopped at a checkpoint in Dimitrovgrad, a town on the border between Serbia and Bulgaria, was travelling towards Macedonia on Friday when the discovery was made.

It was later ordered to go back to Bulgaria, said the customs statement, which did not elaborate on the origins of the radioactive material.