MOSCOW, August 4, 2008 (AFP) - Russia's President Dmitry Medvedev led tributes Monday to Alexander Solzhenitsyn, a 'citizen and patriot' whose writings shaped the 'moral and spiritual' edifice of late-20th century political thought.

Solzhenitsyn, who died at his Moscow home late Sunday aged 89, was 'one of the greatest thinkers, writers and humanists of the 20th century ... an irreplaceable loss for Russia and the whole world,' Medvedev told the writer's family in a telegram, Interfax reported.

'Alexander Isayevich's entire life was devoted to the fatherland. He served the fatherland like a genuine citizen and patriot and he felt with his whole heart for the fate of the Russian people, for justice in the country.

'Alexander Isayevich's constant concern was the formation of moral and spiritual ideals. He believed they were the strongest support for the state and society and he fought for their triumph,' Medvedev added.

Initially a loyal communist, born in the immediate aftermath of the Russian Revolution, Solzhenitsyn was sentenced to eight years in labour camps in 1945 for criticising Soviet dictator Josef Stalin in a letter to a friend, and was only released weeks before the latter's death.

He was published freely under Nikita Khrushchev, but later expelled from the Soviet Union under Leonid Brezhnev in 1974, after authorities discovered manuscripts of his masterpiece on the labour camps, 'The Gulag Archipelago.'

Russia's Prime Minister Vladimir Putin said Solzhenitsyn's death 'is a heavy loss for the whole of Russia. We are proud that Alexander Isayevich Solzhenitsyn was our countryman and contemporary. We will remember him as a strong, brave person with enormous dignity.'

The Soviet Union's last leader, Mikhail Gorbachev, said Solzhenitsyn's works 'changed the consciousness of millions of people, forcing them to think about past and present in a different way.'

'Until the end of his days he fought for Russia not only to move away from its totalitarian past but also to have a worthy future, to become a truly free and democratic country. We owe him a lot,' Gorbachev told Interfax news agency.

French President Nicolas Sarkozy led tributes from outside Russia, echoing the theme of conscience.

'Born a year after the Russian revolution, for the very long years of Soviet terror he incarnated 'dissidence',' Sarkozy said in a statement.

'His intransigence, his ideals and his long, eventful life make of Solzhenitsyn a storybook figure, heir to Dostoyevsky. He belongs to the pantheon of world history. I pay homage to his memory.'

Austrian Foreign Minister Ursula Plassnik said Solzhenitsyn 'proved that we can, without contradiction, be patriotic and still face up to dark episodes of our history.'

The author won the Nobel Prize for literature in 1970, but he refused to travel to Sweden to collect his award, for fear of not being allowed to return to his homeland.

Sweden's Foreign Minister Carl Bildt said Solzhenitsyn was 'a central character in the tragic history of 20th century Russia.

'On days like today, we have a duty to remember him and his commitment to Russia.'

German Chancellor Angela Merkel, who grew up in communist East Germany, said Solzhenitsyn was a 'great and important writer ... who through his work played a decisive role in bringing down the communist totalitarian system.'

Liu Wenfei, a researcher on Russian literature at the Chinese Academy of Social Sciences, said Solzhenitsyn's translated works were used as 1960s 'textbooks' during a time of tense relations between rival ideologies in Moscow and Beijing.

'For Chinese intellectuals, he was a master of literature, and for others who suffered in the 1960s and 1970s, he was a thinker with a deep sense of justice and morality who pitilessly attacked the crimes of the Soviet dictatorship.'

Solzhenitsyn's lying in state will take place on Tuesday ahead of his burial at the Donskoye cemetery in Moscow on Wednesday.