Protesters broke into Serbia’s state television building for the first time in almost 20 years and Albanian police used tear gas to disperse a crowd trying to break into the parliament on a day of anti-government demonstrations across the Balkans.

In Belgrade demonstrators broke into the state-run Radio Television of Serbia (RTS) building on Saturday, demanding to address the population in images aired live.

There have been weekly opposition protests since December against the Serbian president, Aleksandar Vučić, calling for media freedom as a condition for free and fair elections. State television news has given scant coverage to the protests.

“For the past months we have been asking only for one thing – to allow protest organisers to speak on the state television,” said Boško Obradović, the leader of the rightwing Dveri party and one of the people to invade RTS.

Several thousand protesters remained in front of the building as activists chanted “Vučić thief” in the corridors of the building. Anti-riot police later entered the facility and began to take out the demonstrators one by one.

Anti-government demonstrators last stormed the state TV building on 5 October 2000, bringing down the regime of strongman Slobodan Milošević.

Thousands marched peacefully through the centre of Belgrade on Saturday and protests were also held in several other Serbian towns, including second-largest city Novi Sad.

Vučić has previously said he would not bow to opposition demands for electoral reform and increased media freedom “even if there were five million people in the street”, but said he was willing to test his party’s popularity in a snap vote.

An anti-government protester throws a rock at police in the Albanian capital Tirana. Photograph: Malton Dibra/EPA

In Montenegro, thousands marched through the capital Podgorica, the fifth such rally in two months, to demand the resignation of the president, Milo Đukanović, and his government over allegations of abuse of office, graft and cronyism.

Crowds of protesters led by civic and student activists walked through the centre of the city chanting “Milo thief” and “We are the state”.

Đukanović has ruled the tiny Adriatic country for three decades, serving either as prime minister or president.

“We want changes and after 30 years, I think that every citizen understands ... that the last dictator must leave,” said protester Ana Vujosevic.

In Albania’s capital Tirana, an initially peaceful protest became violent when a small number in the several thousand-strong crowd began pushing and throwing stones at police protecting the parliament. Some protesters and police suffered minor injuries.

The protest was the fifth since mid-February as the opposition seeks fresh elections after allegations of corruption and electoral fraud.

Democratic party leader Lulzim Basha said Albania would not have peace until the prime minister, Edi Rama, quits to allow free and fair elections.

“Albania is not destabilised by protests for European values. It has been destabilised by crime and the government’s embrace of it. This we need to end,” Basha said.

Earlier both the European Union, with which Albania hopes to start accession talks in late June, and the United States urged all sides to refrain from violence.

Reuters and Agence-France Presse contributed to this report.