The Kremlin says Russian President Vladimir Putin has told Belarusian President Alyaksandr Lukashenka that Russia is ready to assist Belarus in accordance with a collective military pact, if necessary.
The Kremlin said in the same statement that external pressure was being applied to Belarus. It did not say by whom.
The two spoke on August 16 for the second time in as many days.
Belarus has been rocked by a week of street protests after protesters accused Lukashenka of rigging a presidential election on August 9.
Some 7,000 people have been detained by police across Belarus in the postelection crackdown with hundreds injured and at least two killed as police have used rubber bullets, stun grenades, and, in at least one instance, live ammunition.
Hundreds of those held and subsequently released spoke of brutal beatings they suffered in detention, much of it documented and splashed across social media. Thousands more remain in detention as international outrage mounts.
Facing the most serious threat ever to his authoritarian rule, Lukashenka spoke with Putin on August 15, after saying there was "a threat not only to Belarus."
He later told military chiefs that Putin had offered "comprehensive help" to "ensure the security of Belarus."
The Kremlin said the leaders agreed the "problems" in Belarus would be "resolved soon" and the countries' ties strengthened.