The scandal comes at a bad time for Mr Kuchma

President Kuchma says the tapes are faked and has threatened to sue Socialist leader Oleksander Moroz for defamation.

In early December, a former Kuchma bodyguard announced that he too had material linking the president and his inner circle to the disappearance.

Ukraine's prosecutor-general has questioned both Mr Moroz and Mr Kuchma in connection with the president's accusation of defamation.

Mr Moroz has reportedly said that he is willing to turn his tapes over for independence analysis, but that impartial analysis "is not available in Ukraine".

Independent investigation

The protesters called for an independent investigation into the disappearance of Mr Gongadze, whose online publication Ukrainian Pravda is critical of the government and many leading businessmen.

The missing 31-year-old editor vanished on 16 September.

Georgy Gongadze vanished in September

Police found a mutilated body two months later; the journalist's wife has identified jewellry found with the corpse as belonging to Mr Gongadze, but there has been no official identification yet.

The results of DNA tests are due by the end of the year, the news agency Interfax reported.

The scandal depletes some of the international goodwill Mr Kuchma earned with last week's official closure of the Chernobyl nuclear plant.

And the crisis seems to be coming to a head just as the International Monetary Fund decides whether to release a frozen $2.5bn lending package.