Burundi mystery over ex-rebel chief Rwasa's whereabouts
Burundi's defence minister says he hopes the country's main opposition leader and former rebel leader Agathon Rwasa has not gone into hiding.
His comments follow reports that Mr Rwasa, who signed a peace deal last year to lay down his arms, has not been seen since Wednesday morning.
Earlier this month he withdrew from elections due to be held on Monday.
The election will be the second major vote since the end of the country's brutal 12-year ethnic-based civil war.
Both President Pierre Nkurunziza and Mr Rwasa led mainly Hutu rebel groups fighting against the army which was dominated by the Tutsi minority.
Mr Rwasa refused to end the fighting when other warring factions set up a power-sharing government followed by elections in 2005.
He only led his National Liberation Forces (FNL) in disarming in April 2009 and was widely thought to be the key challenger to President Nkurunziza next week.
Correspondents say tensions have been high since Mr Rwasa and four other presidential challengers withdrew over disputed local elections in May.
Rumours last week that he was about to be detained resulted in several of his supporters being arrested when they rushed to his house in protest.
The authorities say Mr Rwasa left his home before dawn on Wednesday without his usual police guard.
FNL spokesman Jean-Bosco Havyarimana would neither confirm nor deny whether Mr Rwasa had gone into hiding, saying he was on holiday.
"I do not personally have the authority to track him wherever he goes.... All I know is that he has a 15-day leave from service. So he does not report to work," he told the BBC's Focus on Africa programme.
Defence Minister Germain Niyoyankana said following the opposition's rejection of the district elections there had been a spat of grenade attacks.
"The situation is still under control. But is there a risk it can get worse? Of course there's a risk," he told reporters in Bujumbura.
"The same Burundians who were responsible for the crisis we went through are still around. They may still have they same mindset."
An estimated 300,000 people are believed to have died during the civil war.