Putin has unexpectedly revived efforts to create a single state from the two former Soviet republics - a merger that would expand his options for exercising power after he steps down from the Russian presidency next year, the AP reports.
Putin heads to the Belarusian capital, Minsk, on Thursday for discussions of a framework for the long-debated union, fleshing out an existing agreement that has meant little in practice.
A merger of Russia and Belarus could allow Putin to leave the Russian presidency as promised in May yet still remain a chief of state.
"I wouldn't be surprised if Putin tries to speed up a union with Belarus ... to become the president of the unified state," said Gennady Zyuganov, Russia's Communist Party chief.
Putin, who has indicated he will seek to retain significant influence after term limits force him from the Kremlin, does have at least one other option.
On Monday, he said he supported his protege, first deputy prime minister Dmitry Medvedev, to become Russia's next president. Medvedev instantly became the overwhelming favorite in the March 2 vote and he, in turn, asked Putin on Tuesday to be his prime minister, though Putin has not yet accepted.
The creation of a single state could give Putin an alternative to the Russian prime minister's post.
If the two countries can agree, it would mark the first merger of a former Soviet state with Russia since the Soviet Union split apart in 1991 - a step that would make many Russians proud.
But the move could damage Russia's relations with the West, especially if Moscow is seen as using pipelines that supply Belarus with natural gas to force the smaller country into an agreement.
Ahead of Putin's visit, Belarus' beleaguered Western-oriented political opposition was already fighting the idea of a merger. Police on Wednesday forced some 200 protesters from a Minsk square where they waved flags and chanted "No union with imperial Russia !"
One of the leaders of the opposition Young Front was knocked off his feet and stomped on by riot police. He was bundled into an ambulance, unconscious.
Some analysts doubt a deal can be reached, because Belarus President Alexander Lukashenko - a Soviet-style leader dubbed Europe 's last dictator by the West - is unlikely to cede power.
Lukashenko's office said last week the talks between Putin, Lukashenko and other ranking officials would focus on a draft constitution of a union.
Russia's Ekho Moskvy radio quoted unidentified members of the Lukashenko administration as saying Moscow and Minsk had struck a deal: Putin, the sources said, would become president of a Russia-Belarus union while Lukashenko would become the speaker of its parliament.
Officials in Moscow and Minsk have denied the report, but politicians and commentators in both countries agree that Putin's trip signals a renewed interest in the merger.
When Medvedev proposed that Putin become prime minister, many analysts saw it as the Kremlin's preferred plan to maintain his influence. But some said Putin would never accept what would amount to a demotion.
Pavel Borodin, secretary of the existing Russian-Belarusian executive body, said Wednesday that drafts of the constitution being considered would give the president of a new unified country the power to rule over the current national governments.
He said the new constitution would be subject to approval by each nation's parliament and would be put to voters in national referendums.
Putin could find it difficult to persuade the Belarusian leader to relinquish his country's independence. And Lukashenko seems to lack the leverage needed to win an agreement that favors Belarus, which has a population of just 9.7 million compared with Russia's 141.4 million.
"Putin and Lukashenko have sought to outmaneuver and cheat one another over the past few years," said Fyodor Lukyanov, the editor of Russia in Global Affairs magazine.
Russia and Belarus signed a union agreement in 1996 that envisaged close political, economic and military ties, but efforts to achieve a full merger have foundered.
In the 1990s, Lukashenko pushed for the creation of a single state, apparently hoping to take the reins from Russia's ailing President Boris Yeltsin. Putin's election in 2000 demolished Lukashenko's hopes to rule both countries.
Two years later the Belarusian leader angrily rejected a Kremlin proposal for incorporating his nation into the Russian Federation - leaving him without a job.
Bilateral relations soured. Lukashenko described Russia as a "huge monster," saying Moscow's actions were worse than those of Nazi Germany, which reduced much of Soviet Belarus to ruins in World War II.
If Lukashenko refuses to cede control, the Kremlin could try to force his hand by using its most powerful weapon: energy.
At the year's start, Russia more than doubled the price of natural gas and imposed a customs duty making oil more expensive. To pay its bills, Belarus was forced to sell half of its national gas pipeline company to Gazprom, Russia's state gas monopoly.
In August, Gazprom threatened to halt future natural gas shipments if Belarus failed to pay what it already owed.
The two sides negotiated a settlement, but the threat of a further increase in energy prices still looms over Belarus ' heavily subsidized, Soviet-style economy.