In comment of the release of Belarusian opposition figures Andrey Sanikov and Dmitry Bondarenko, Kubilius said it was "not the first step of this type."
"They are sent to prisons and a bit later they are released in hopes of a large number of positive responses," he told journalists after the government's meeting on Monday.
"I can only applaud the decision but, as far as we understand, some political prisoners remain behind the bars," he added.
In the prime minister's words, the changes in Belorussian policies in the fields of human rights and democratic elections "are far from the progress that we have been striving for."
"Every time we assess the Belorussian situation together with partners in the European Union and do everything in our capacity to see things in Belarus change for the better," Kubilius added.
Belarus' opposition leader, Sanikov, was unexpectedly pardoned of his five-year jail term on Sunday. He was sentenced after challenging Lukashenko. Bondarenko, another prominent opposition activist, was released on Sunday. He had been arrested amid Lukashenko's drive of rigid measures against opposition figures.
The two were freed from prison after the European Union stepped up pressure on Minsk for release of all political prisoners. The EU also introduced new sanctions against Belarus' top-ranking officials.
Sanikov, Belarus' former foreign minister, was one of Lukashenko's main opponents in the presidential election in December 2010, which triggered mass opposition demonstrations following Lukashenko's victory.
The activist was detained amid the administration's efforts to dispel a mass demonstration on 19 December that was held in protest of re-election of Lukashenko. More than 600 people were arrested, including nearly all opposition candidates.
Last May, Sanikov was found guilty of organizing mass riots and sentenced to five years in prison.
Bondarenko was put in prison for two years for serious violation of public order.