Belarusian President Alexander Lukashenko said Russia has agreed to offer security assistance in the event of external military threats.
Lukashenko also expressed his concerns about the NATO military exercises taking place in neighboring Poland and Lithuania.
The news comes as the beleaguered president faces mass protests against the disputed August 9 elections.
Thousands of people rallied outside public television on Saturday, demanding full coverage of the protests.
The unrest erupted after President Alexander Lukashenko won a landslide election victory last week, the outcome of which was doomed amid widespread allegations of vote rigging.
The Central Election Commission said Lukashenko, who has been in power since 1994, won 80.1% of the vote and the main opposition candidate Svetlana Tikhanovskaya 10.12%.
But Ms Tikhanovskaya insists that where the votes were correctly counted, she garnered support ranging from 60% to 70%.
What is happening politically?
As the unrest continued on Saturday, Lukashenko sought help from Russian President Vladimir Putin.
Lukashenko said President Putin had promised to provide what he called comprehensive assistance in the event of external military threats against Belarus.
The announcement came the day after EU foreign ministers agreed to prepare new sanctions against Belarusian officials responsible for “tampering.” The United States also condemned the election as “not free and fair.”
In a joint statement on Saturday, the prime ministers of three Baltic republics – Latvia, Lithuania and Estonia – “expressed their deep concern at the violent repression … and the political repression of the opposition by the authorities”.
Lithuania and Latvia have previously said they are ready to play a mediating role in Belarus, provided the authorities stop violence against protesters and form a national council with members of civil society. They warned that the alternative was sanctions.
The leaders said the presidential election was “neither free nor fair” and called for a “transparent” vote “with the participation of international observers”.
What’s the latest with the protests?
Protests continued after Ms Tikhanovskaya called for more peaceful gatherings on Friday.
Around 100 staff came out of the public television building to join Saturday’s protests, saying they were planning a strike on Monday, AFP news agency reports. Others signed a letter in favor of a strike.
“Like everyone else, we demand free elections and the release of those detained during mass protests,” employee Andrei Yaroshevich told AFP.
On polling day, Belarusian state channels broadcast the voices of Lukashenko supporters and did not cover the protests. State television then showed footage of violence to blame the protesters and warn people not to participate.
Several journalists have resigned because of the coverage.
Earlier on Saturday, thousands of people waved flags, lit candles and laid flowers at the scene near the metro station where one of the protesters, Alexander Taraikovsky, died on Monday.
Others held up photos of injured protesters, as drivers hooted their horns.
Many opposition supporters chanted “Go! – a call for the resignation of President Lukashenko – and some carried signs with slogans against police violence.
The circumstances of Mr. Taraikovsky’s death are unclear.
Officials claim he died when an explosive device detonated in his hand during a protest, but his partner, Elena German, told the Associated Press news agency she believed the man from 34 years old had been shot by police.
A “March for Freedom” is also planned in the center of the city on Sunday, a week after the disputed election.