KYIV, Ukraine (AP) — Thousands of aged pensioners marched Monday in the capital of Belarus to demand the resignation of the authoritarian president, who has been under pressure of daily demonstrations for nearly three months.

The demonstrators, estimated at about 4,000 by the human rights group Viasna, also called for the release of people arrested during the protests whom it considers political prisoners.

More than 15,000 people have been arrested since the protests began after the Aug. 9 presidential election in which Alexander Lukashenko was declared to have won a sixth term. Most served short jail terms or were fined, but human rights activists say about 100 of those arrested should be considered political prisoners.

Authorities indicated Monday that pressure on protesters is intensifying, saying that more than 230 people arrested in a demonstration on Sunday would face charges that could bring up to three years in prison.

Protesters and some poll workers say the results of the presidential election were manipulated. The claims galvanized discontent with Lukashenko's repressive 26-year rule and set an unprecedented wave of large and persistent protests.

Lukashenko has consistently refused to negotiate with opponents, a standoff that raises questions about how long the opposition can continue to bring people into the streets. Although demonstrations on Sundays have typically attracted crowds of 100,000 or more, the most recent Sunday protest saw a turnout of only about 20,000.

About 300 people were arrested in that demonstration, in which police fired in the air and used stun grenades against the crowd.

All prominent members at the helm of the opposition’s Coordination Council, which was formed to push for a transition of power, have either been jailed or left the country. One more activist on the Council, Denis Gotto, was detained during Sunday’s demonstration.

Lukashenko has scoffed at suggestions of dialogue with the opposition and instead intensified the crackdown on protesters, ordering officials to expel students from universities for participating in demonstrations and to take action against plant workers that go on strike.