VIKTOR YUSHCHENKO, the President of Ukraine, suffered his biggest blow since taking office when his chief of staff resigned in the latest sign of a rift between the leaders of the Orange Revolution.

Oleksandr Zinchenko, who masterminded Mr Yushchenko’s election campaign and the protests that helped sweep him into power, tendered his resignation in a terse two-paragraph statement without explaining his reasons.

He is due to hold a news conference today, in which he is expected to shed light on the mounting tensions between Mr Yushchenko, Yuliya Tymoshenko, the Prime Minister, and the other Orange Revolution leaders.

Mr Yushchenko’s office said in a statement: “The Ukrainian President has accepted the resignation of Ukraine State Secretary Oleksandr Zinchenko.” The President “recently had a difficult conversation with the head of the secretariat and put before him specific assignments with the aim of improving the level of work and increasing the professionalism of the presidential apparatus”.

Mr Zinchenko’s apparently acrimonious departure will lend weight to critics who say that Mr Yushchenko is failing to deliver the reforms that he promised, because of in-fighting. Mr Yushchenko took office in January promising to root out the official corruption and economic mismanagement that had plagued Ukraine since it won independence from the Soviet Union in 1991.

But many of his reforms appear to have run aground amid squabbling between his office and that of Mrs Tymoshenko, with whom he forged an alliance last year to oust the entrenched post-Soviet elite. In February, Roman Zvarych, the Justice Minister, threatened to resign after a clash over the Government’s oil policies, but was persuaded to stay after talks with Mr Yushchenko.

Last month, Mr Yushchenko himself came under fire after reporters revealed that Andriy, his 19-year-old son, drove a top-of-the-range BMW and spent hundreds of dollars in fashionable Kiev nightspots. It later emerged that the President’s son owned the rights to the logos and slogans that helped to sell the Orange Revolution.

Last week Mikhail Brodsky, who is an adviser to Mrs Tymoshenko, accused the President’s entourage of trying to enrich themselves in the re-privatisation of assets allegedly sold in shady deals under Leonid Kuchma, the previous President.

Mr Brodsky said in an interview on Ukrainian television: “I declare that there is nothing but corruption around Yushchenko.”Markian Lubkivsky, Mr Zinchenko’s own deputy, announced on Friday that the presidential administration was “on the threshold of significant changes”, and needed to improve its co-ordination with the rest of the Government.

Mr Zinchenko, 48, is a former deputy speaker of parliament who was previously aligned with Mr Kuchma. He was a senior party official in the Ukrainian Socialist Party (United), headed by Mr Kuchma’s former chief-of-staff, Viktor Medvedchuk.

But he was kicked out of the party in 2003, reportedly over disagreements about the Medvedchuk-controlled Inter television station, and joined Mr Yushchenko’s camp.

The Ukrainian media reported last week that Mr Zinchenko might be named ambassador to Russia, but he denied those reports.

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