Burundi has been in crisis since President Pierre Nkurunziza announced in April he planned to run for a third term
* Shootings, explosions overnight in capital
* Police arrest 28 youths suspected of being armed
* One killed in shootout in province near Rwanda
* Mortar attack on state transmitting station (Adds police comment, mortar attack on state broadcaster transmitter)
NAIROBI, Nov 22 (Reuters) - At least five people were killed in overnight clashes in Burundi, police said on Sunday, denying residents' reports of shelling late at night at the president's office in the capital Bujumbura.
Burundi has descended into violence since President Pierre Nkurunziza announced in April he would run for a third term -- a move opponents said violated the constitution -- and went on to win a disputed election in July.
The authorities have identified those behind the unrest only as "criminals", but the leader of a failed coup against Nkurunziza, General Leonard Ngendakumana, said in July that force was the only way to prevent the president's third term.
Deputy police spokesman Moïse Nkurunziza said there was no shelling near the president's office in the Rohero district of the capital on Saturday. Residents had reported clashes between soldiers at the presidency and unknown attackers.
"Up to now the police has no information of a likely shelling last night," Nkurunziza told a news conference.
Hundreds have been killed in related violence since April and 217,000 people have fled to surrounding countries, raising fears of slide into ethnic conflict in a region where memories of the 1994 genocide in neighbour Rwanda are still raw.
His opponents say Nkurunziza's third term also violates a peace treaty that ended a 12-year civil war in 2005.
A military officer who requested anonymity said unidentified men fired mortars at a state-run radio and television transmitting station in Bujumbura on Sunday afternoon, damaging one parabolic antenna. A soldier at the site said one soldier was wounded in the attack.
Bujumbura Mayor Freddy Mbonimpa said four people had been killed across the capital since Saturday, with two policemen wounded and 28 people arrested on suspicion of holding weapons.
But residents said the youths arrested in a police raid on a bar in Bujumbura's Ngagara neighbourhood were unarmed and just old school friends gathering before a wedding.
Later that evening, protesters took to the street in Ngagara, shouting: "Nkurunziza out, we will never accept your illegal third term."
A resident reported that this was followed by the sound of gunfire and explosions, though Reuters could not independently verify this.
Police in Kirundo, a province bordering Rwanda, said a bystander was killed in a shootout between a gunman and police at a bar.
Last week, the United Nations Security Council asked Secretary-General Ban Ki-moon to report within 15 days on options for boosting the U.N. presence in Burundi. (Additional reporting by Patrick Nduwimana in Bujumbura; Writing by George Obulutsa; Editing by Raissa Kasolowsky)
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