Protesters have taken to the streets of Burundi for a second day after activists said that at least five people were killed during clashes with police a day earlier.

The protests began on Sunday in the capital, Bujumbura, following the president's plan to run for a third term, a move critics say violates the constitution, which limits leaders to two terms in office.

Burundi's ruling CNDD-FDD party nominated the incumbent Pierre Nkurunziza as its presidential candidate on Saturday, prompting hundreds of civil society groups to condemn the move.

Al Jazeera's Malcolm Webb, reporting from Bujumbura, said the city centre was quiet on Monday but that there had been protests in several other suburbs.

"Massive crowds of about a few hundred people have been gathering. They are not doing anything," he said.

Police broke up a march of around 1,000 youths trying to reach Burundi's capital, an AFP news agency correspondent said.

In some areas protesters have erected roadblocks where they have been demonstrating. Police have fired tear gas to break up the protests. But people are dispersing and regroup elsewhere, our correspondent said.

He said some people had suffered bullet wounds as well.

"The protesters are showing no signs that they are backing down, and the president is showing no sign that he will back down from his intention to stand for re-election," he said.

Escalation fears

Al Jazeera's Webb said there were fears that the situation could escalate if former rebel groups mobilised their fighters.

While he could not confirm any evidence of this, he said there had already been reports of unidentified plainclothes men among the police personnel.

The ruling CNDD-FDD party has been accused of intimidating opponents in the run-up to the June 26 presidential election.

Pierre Claver Mbonimpa, a prominent activist, said at least five people were killed in Bujumbura on Sunday, three of them in protests and two more in an attack by the CNDD-FDD's Imbonerakure youth wing.

Nkurunziza has been in power for two terms since 2005, and opposition figures and rights groups say his attempt to stay put is unconstitutional.

They also pledged to step up the protests, despite a government ban on demonstrations and threats to call out the army.

"This time we will not back down," one demonstrator said, promising to push through to the city centre.

Relatives of Sunday's bullet-wound victims told AFP that they were shot at close range by the police.

But speaking on state television, Saidi Juma, Bujumbura's mayor, claimed that those who died had been killed by the demonstrators.

Source: Al Jazeera and agencies