"I very much hope that the government of Belarus will reciprocate, beginning the reforms their people need and ending their self-imposed isolation."
But in Minsk hundreds of police, special forces officers and paratroopers closed off access to Oktyabrskaya Square, the capital of Belarus on Sunday.
Demonstrators, though, were able to gather about two kilometers away from the intended meeting point.
"Europe's last dictator"
Barroso said he believed EU assistance to Belarus "could be significantly increased and would thus help improve the quality of life of Belarussians".
Alexander Lukashenko, Belarus's president, is facing the increased economic pressure from Russia, the country's traditional ally, which raised gas and oil prices for Belarus this year.
Dubbed "Europe's last dictator" by his critics, he has begun to speak increasingly about improving ties with European nations.
Last year's annual protest march on what the opposition calls Freedom Day, the anniversary of the 1918 declaration of the first Belarusian state, ended with police detaining hundreds of demonstrators and claims that some of them were beaten.
Alexander Milinkevich, the opposition leader, said interest in this year's rally was not as high as it had been last year when the march marked the culmination of an unprecedented week of protests against Lukashenko's disputed re-election to a third term.
"Today, the mood of the people isn't like it was a year ago when people believed in a quick change," Milinkevich said.
In the run-up to the opposition rally, the opposition said that at least 34 activists had been arrested or detained and that hundreds had been ordered not to come to Minsk.
State-controlled television broadcast a news segment on Saturday night that warned of administrative fines and possible criminal action for violation of public order.
The broadcast also emphasised that this would included participation in non-sanctioned rallies, though the news report never directly mentioned the opposition's planned rally.