Belarusian President Alexander Lukashenko says that Russia has agreed to offer security assistance in the case of external military threats.
Mr Lukashenko also voiced concerns over Nato military exercises taking place in neighbouring Poland and Lithuania.
The news comes as the embattled president faces mass protests over the disputed 9 August election.
Thousands gathered outside state television on Saturday, demanding full coverage of the demonstrations.
The unrest erupted after President Alexander Lukashenko claimed a landslide victory in last week’s election, the result of which has been condemned amid widespread allegations of vote-rigging.
The Central Election Commission says Mr 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 votes were properly counted, she won support ranging from 60% to 70%.
What’s happening politically?
As the unrest continued on Saturday, Mr Lukashenko sought help from Russian President Vladimir Putin.
Mr Lukashenko said President Putin had promised to provide what he called comprehensive assistance in the event of external military threats to Belarus.
The announcement came the day after EU foreign ministers agreed to prepare new sanctions against Belarusian officials responsible for “falsification”. The US has also condemned the election as “not free and fair”.
In a joint statement on Saturday, meanwhile, the prime ministers of three Baltic republics – Latvia, Lithuania and Estonia – “expressed deep concern at the violent crackdown… and the political repression of the opposition by the authorities”.
Lithuania and Latvia have previously said they are prepared to mediate in Belarus, provided the authorities stopped violence against protesters and formed 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”.
“The prime ministers urge the Belarusian authorities to refrain from violence against peaceful demonstrators [and to] re