President Pierre Nkurunziza set a Nov. 7 deadline on Monday for Burundians to hand over illegal firearms or risk being "dealt with as enemies of the nation", after months of protests over his re-election in July and a failed coup.
Burundi, which emerged from civil war a decade ago, was thrown into turmoil over Nkurunziza's plan to seek a third term in office, which many of his critics said was unconstitutional.
The bid, which Nkurunziza ultimately won in a disputed vote, plunged the country into crisis, including violent clashes between protesters and security forces in the capital Bujumbura and a series of targeted killings.
Experts say "tit-for-tat" assassinations of government officials and members of the opposition risk driving the nation back into another conflict and could reopen old ethnic wounds.
Burundi lies next to Rwanda, scene of a 1994 genocide.
In Monday's address to the nation, Nkurunziza said people had five days to voluntarily give up their guns.
"Those who will not do so... will be taken as criminals and be prosecuted according to the anti-terrorism law and be dealt with as enemies of the nation," Nkurunziza said. "This is the last call we make."
He said that individuals who comply will "be trained on patriotic education" and returned to their families.
Nkurunziza also called on police to restore peace and security across the capital Bujumbura within a month.
"In addition, you are allowed to use all the necessary means and authorized rules and regulations in security matters," he said.