Heavy gunfire has been heard after police fired teargas at protesters throwing stones in a suburb of Burundi's capital Bujumbura during a demonstration against the president's bid for a third term.

It was not immediately clear who fired the shots during Tuesday's clashes in Butarere district, where hundreds of protesters had gathered claiming Pierre Nkurunziza's third election run violated the constitution and a peace deal that ended civil war in 2005.

Protesters grabbed one policewoman and beat her up, accusing her of firing at them, a witness told Reuters news agency. She was later released, after sustaining injuries.

East African leaders, including Nkurunziza, will meet in Tanzania on Wednesday to discuss the crisis and rising tensions in a region with a history of ethnic conflict.

Al Jazeera's Malcom Webb, reporting from Nyakabiba, on the outskirts of Bujumbura, said protesters have been out in large numbers to put pressure on the region's leaders in advance of the summit.

"People here are very keen to get their message heard before heads of states from East Africa meet in Tanzania tomorrow," he said.

Peace summit

During more than two weeks of protests that have plunged Burundi into a crisis, police have fired in the air and have been seen shooting in the direction of protesters.

Police deny shooting any demonstrators.

INSIDE STORY: Burundi on the brink?

At least 19 people have been killed so far. More than 50,000 people have fled Burundi to neighbouring states seeking safety.

The US, which provides support to the army, has demanded that police stop using "violent force" against protesters.

Nkurunziza has said he would press on with his election bid, although the US, other Western nations and several African countries have urged him not to run.

The EU and others have suspended or are reviewing some aid, saying violence must stop.

The constitution and the Arusha peace deal, which ended a conflict that pitted Burundi's majority Hutu ethnic group against minority Tutsis, both set a two-term presidential limit of five years each.

A constitutional court ruled that Nkurunziza's first term did not count because he was picked at the time by legislators not chosen in a popular vote.

Opponents say the court is biased and the UK, one of Burundi's donors, has also questioned the court's neutrality.

Source: Al Jazeera and agencies