Small groups of protesters resumed demonstrations on Monday against Burundi's President Pierre Nkurunziza and his bid for a third term, days after he survived an attempted coup.

The atmosphere was tense as soldiers deployed on the streets of Bujumbura where more than 20 people were killed in almost three weeks of protests before the failed putsch, a Reuters witness said.

Nkurunziza's bid for another five years in power -- which both the generals who mounted the coup and the protesters say is unconstitutional -- has plunged Burundi into its worst crisis since an ethnically charged civil war ended in 2005.

More than 100,000 refugees have fled to neighbouring Rwanda, Democratic Republic of Congo and Tanzania, fearing political tensions will take on an ethnic hue and trigger an all-out conflict between the Hutu majority and Tutsi minority that could engulf Africa's Great Lakes region.

Although Nkurunziza's position appears to be stronger after the rump of the army rallied round him, last week's attempted coup by sacked former intelligence chief Godefroid Niyombare, now behind bars, has done nothing to resolve the political dispute.

On Monday, Kenya called for the presidential elections scheduled for June 26 to be postponed to allow for a "conducive environment" but said they still had to be held before the end of August, when Nkurunziza's term officially closes.

Fear over the unrest are particularly acute in Rwanda, which has the same ethnic mix as Burundi and which was torn apart by a genocide in 1994 that killed 800,000 mostly Tutsis and moderate Hutus.

On Sunday, at his first public appearance since the coup attempt, Nkurunziza made no reference to the political crisis, saying instead he was "very preoccupied" by the threat posed by Somali militant group al Shabaab.

Burundi contributes forces to an African Union force fighting al Shabaab in Somalia -- and the militants have launched attacks in other African countries involved in the mission.

But the al Qaeda-linked Somali group dismissed his statement, saying he was just trying to divert attention while he prepared "mass revenge" on his domestic opponents.

Nkurunziza's opponents argue that his bid violates a two-term limit in the constitution and the spirit of the 2005 Arusha peace agreement that ended the civil war.

He argues that his first term does not count because he was appointed by parliament, not directly elected, and points to approval from the constitutional court. His opponents and some donors have questioned the court's impartiality.

-Reuters-