Twelve years on, Ukraine still has not committed itself to a closure date, saying that $1.2bn of Western aid is needed for alternative power supplies.

During his talks with Ukrainian President Leonid Kuchma, the American Vice President tried to persuade Ukraine to live up to earlier promises, and close Chernobyl down for good by the year 2000.

The sarcophagus contains tons of toxic material

"I believe that this is imperative for the safety of the Ukrainian people, the safety of Europe and the well-being of the world for the remaining reactor now operating at Chernobyl to be shut down as soon as it is feasible to do so," Mr Gore said.

But Mr Gore has been unable to tie down the Ukrainian President to a date.

A BBC correspondent says that power sources are scarce in the country, and officials there are worried about future supplies.

To replace the remaining reactors of Chernobyl, they would need to complete two other nuclear reactors in Western Ukraine - and secure more than $1bn Western aid.

A first hand inspection

Mr Gore, who during his visit has identified the environment as a key political priority, travelled to Chernobyl on Thursday to inspect the site at first hand.

He flew over the power plant by helicopter, but later examined the concrete shelter at ground level, which had been built around the remains of reactor four.

Now crumbling, the concrete "sarcophagus" holds tons of highly radioactive fuel and contaminated dust and debris.

Scientists fear that if the deterioration of the shelter continues, this toxic material could spill out into the water system and surrounding countryside.

Mr Gore also visited the place where Ukrainians say "time stood still" - the town of Pripyat, once built to house 50,000 Chernobyl workers, but now a ghost town.

Its population was evacuated at the time of the disaster.

Mr Gore toured the area in an ordinary suit, but US officials said such a brief visit did not pose any danger to his health.

However, prioir to his arrival American medical teams were scouring the site for days looking for radiation "hot spots".