Some of the buildings at the reactor site near Kiev in Ukraine are unstable and need to be propped up urgently before any new work starts, the experts say. The only safe way to contain the radioactive remains of the reactor is to build a huge new "sarcophagus" which would cover not only Unit 4 - the one that exploded in 1986 - but also the adjoining Unit 3, which is still operating.
After the explosion, which sent radioactivity around the world, the Soviet Union erected a giant containment, known as the sarcophagus, around the wrecked reactor.
But the European group found it was unstable, was not designed to withstand earth tremors and allowed rain and wind into the building, so it does not even properly contain the remaining radioactivity.
Worse still, the instability of the sarcophagus is threatening the integrity of a common services building between Reactor 4 and its neighbour. This building is fundamental to the safe operation of Unit 3, but is itself unstable and not designed to withstand shocks.
The EU group recommended that Unit 3 be shut down and both reactors covered by a new airtight building that would have to be strong enough to stand for 100 years and big enough to allow complete dismantling of the structures within it.
Ukraine has denounced the report as Western pressure to close the remaining Chernobyl reactors, which generate 7 per cent of the country's electricity. President Leonid Kuchma visited the station this month and said it was up to the international community to work out a plan if it wanted Chernobyl closed.