Mr Yeltsin, 67, returned from two weeks' sick leave on Monday, and promptly dismissed chief of staff Valentin Yumashev.

In addition, Mr Yeltsin announced he was taking personal control of the ministry of justice and the tax police.

Hours later, the president was back in hospital.

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His spokesman told reporters that Mr Yeltsin was to complete a course of treatment for pneumonia, the same illness that caused his earlier absence from work.

The Kremlin has not yet commented on the morning's developments, which took Moscow by surprise.

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Our Moscow Correspondent Rob Parsons says it remains to be seen how Mr Yeltsin will deal with the extra work involved in taking on two new ministries while there are still doubts surrounding his state of health.

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Mr Yumashev, a close aide and personal friend to Mr Yeltsin, was replaced by Nikolai Bordyuzha, secretary of the president's advisory body, the Security Council. Mr Bordyuzha will keep his present job as well as taking on the new one.

Mr Yumashev's deputies, Yuri Yarov, Mikhail Komissar and Yevgeny Savostyanov also lost their jobs .

Communications chief fired

Among other staff sacked by Mr Yeltsin was the head of the Federal Agency for Government Communications and Information, Alexander Starovoitov. He has been replaced by Vladislav Sherstyuk.

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It has been suggested that Mr Yumashev - who previously controlled all access to the president and his family - lost favour with Mr Yeltsin after making negative comments about the president's state of health.

Mr Yumashev and other aides had said openly that the president was too sick to handle the running of Russia.