Ukraine said on Wednesday its borders remained open to Belarusian citizens but Kyiv would deal harshly with any attempt by Belarusian or Russian intelligence services to abuse that openness.
Ukrainian Foreign Minister Dmytro Kuleba, speaking in Lisbon, said any strengthening of Russia's position in Belarus as a result of the crisis posed a threat to Ukraine's national security.
"Though the border with Ukraine is free and open to the citizens of Belarus we will harshly react to any attempts to use, to abuse the openness of Ukraine by Belarusian or Russian intelligence services," he told a news conference in the Portuguese capital. He did not elaborate.
Belarus has been rocked by mass protests since the re-election of veteran President Alexander Lukashenko in an Aug. 9 election his opponents say was rigged.
Kuleba's comments came after allies of Belarusian opposition leader Maria Kolesnikova said she had thwarted an attempt to deport her by tearing up her passport to avoid being forced to cross the border into Ukraine.
Two other opposition leaders were however removed to Ukraine by the Belarusian authorities, they said.
"We have serious reasons to believe that these people did not enter Ukraine voluntarily," Kuleba said.
Ukraine, which has already frozen contact with Belarus wanted an independent, sovereign Belarus, where democracy and a market economy flourish, he said.
Kyiv has joined the European Union in condemning the recent elections in its northerly neighbour as not free or fair.
The Belarus crisis has strained Kyiv's relations with Russia, whose Foreign Minister Sergei Lavrov last week accused Ukraine of fomenting trouble in Belarus, an accusation Ukraine denied.