It is the worst violence seen in the capital since 2015
(Changes word in second paragraph to clarify timeline)
At least 135 people have been injured in the worst outbreak of violence in years in the Central African Republic's capital, aid agencies said on Friday, straining hospital trauma centres.
At least 21 people died in clashes this week when United Nations peacekeepers and local security forces battled armed groups in Bangui's PK5 neighbourhood - a Muslim enclave of the majority Christian city - over three days, a local official said.
Medical charity Medecins Sans Frontieres (MSF) said it had treated 83 people since the weekend at a hospital and a health centre, while the Red Cross said 52 injured had arrived at another hospital.
It is the worst violence seen in the capital since 2015, said MSF's operational manager William Hennequin.
"We are worried to see such level of violence and the impact it could have outside Bangui," he told the Thomson Reuters Foundation.
He said there might be more injured people in the PK5 neighbourhood, though it is currently calm.
"We are watching and preparing in case we have to treat more wounded."
The country has been gripped by conflict since rebels ousted the former president in 2013, sparking reprisals from rival militias. However, fighting rarely breaks out in the capital.
The International Committee of the Red Cross (ICRC) said it was ready to put up tents if needed outside Bangui's Community Hospital, where the trauma unit and casualty ward are full.
The wounded included fighters as well as civilians who were hit by stray bullets, said ICRC spokeswoman Jessica Barry.
Hundreds of angry protesters on Wednesday laid the bodies of at least 16 people killed in front of the headquarters of the peacekeeping mission, accusing U.N. troops of firing at civilians during their operation in PK5.
The head of U.N. peacekeeping said civilians killed were young people who had been "manipulated" and armed by criminal gangs to confront the peacekeepers and Central African Republic forces.
Reporting by Nellie Peyton, Editing by Robert Carmichael.