The Kremlin moved to quash talk of such a possibility, denying that Mr Putin's talks with Belarusian President Alexander Lukashenko and other officials would touch upon a draft constitution aimed at describing the structure of a unified country's government.

But Mr Lukashenko's office said last week that the document would be part of the agenda, and the secretary of the existing Russia-Belarus executive body had said it would likely be discussed.

Many politicians and observers in both nations said Mr Putin's unusual visit to Belarus signalled his renewed interest in the long-debated merger plan. 'I wouldn't be surprised if Putin tries to speed up a union with Belarus ... to become the president of the unified state,' Russian Communist Party chief Gennady Zyuganov said this week.

Mr Putin, who has indicated he aims to retain significant influence after term limits force him from the Kremlin in May, does have at least one other option.

He said he supported his protege Dmitry Medvedev to become Russia's next president. Mr Medvedev instantly became the overwhelming favourite in the March 2 vote and he, in turn, asked Mr Putin to be his prime minister, though Mr Putin has not yet accepted.

The creation of a single state could give Mr Putin an alternative to the Russian prime minister's post, potentially creating a job that would place him above national presidents.

A merger of the two predominantly Slavic, Russian Orthodox countries would be the first of any two former republics since the Soviet Union split apart in 1991, and would make many Russians proud. But it would deepen western concerns about an increasingly assertive Russia.

The Kremlin said that a draft constitution of a union was not on the agenda of yesterday's session of the Supreme State Council of the Union State. Mr Putin dined privately with Mr Lukashenko after his arrival.

Last week, Russian radio quoted unidentified members of the Lukashenko administration as saying Moscow and Minsk had struck a deal under which Mr Putin would become president of a Russia-Belarus union, while Mr Lukashenko would be speaker of its parliament.

Pavel Borodin, secretary of the Russian-Belarusian executive body, said drafts of the constitution being considered would give the president of a new unified country the power to rule over national governments.

He said the new constitution, once agreed upon by governments, would be subject to approval by each nation's parliament and put to voters in national referendums.

Some analysts doubt a merger deal could be reached, saying Mr Lukashenko - a Soviet-style leader dubbed Europe's last dictator by the west - was unlikely to cede power.

'The two nations have opposite interests,' said Alexander Klaskovsky, an independent political analyst who is based in Minsk. 'Moscow wants to expand its presence in Belarus, while Minsk wants to get economic assistance while maintaining full sovereignty.'

Russia and Belarus signed a union agreement in 1996 that envisaged close political, economic and military ties, but a full merger has not eventuated. In 2002, the Belarusian leader rejected a Kremlin proposal to incorporate his nation into Russia. For the second day, Belarusian authorities dispersed demonstrators protesting against a merger. About 15 young people protested briefly in central Minsk, with signs saying 'Putin go home' and 'No union with Russia'.