Russian President Dmitry Medvedev has fired one of his top advisors for abuse of office in one of the biggest changes to his Kremlin administration since taking power, media reported on Thursday.

Mikhail Lesin, media advisor to Medvedev, "was relieved of his duties at his own request", the Kremlin said in a statement posted in its website without giving further details.

But a source in the presidential administration told the Interfax news agency that Lesin had departed his job due to "failure to observe the rules and ethical behaviour of state service".

He had also used his "official position for solving questions not connected with official duties," the source added.

Since taking over from Vladimir Putin as president in May last year, Medvedev has repeatedly vowed to cut corruption in Russia and end abuses of power by officials.

However he has yet to make major changes to the administration he inherited from Putin and some analysts have criticised the president for not following his rhetoric with actions.

Business daily Vedomosti said that the sacking has been initiated by Medvedev himself because Lesin's extensive business interests in the media had caused a conflict of interest.

The daily Kommersant described Lesin's departure as the "first serious resignation from the administration of President Dmitry Medvedev."

"It is also the first time in a decade that a high-ranking official is fired with such a harsh statement," it added.

Lesin, who took up the post in 2004 under the Putin presidency and had also held top positions under former president Boris Yeltsin, is seen as a man close to the current strongman prime minister Putin, Vedomosti said.

Medvedev's rise to power sparked hopes he would adopt a more liberal stance than Putin but analysts have struggled to detect a major difference between the two men.

Some commentators are now arguing that the president is taking a more independent line, particularly after a state-of-the nation address last week in which he called for wholesale reform of the Russian economy.