Attackers wielding guns and machetes have killed 22 people in an assault on Muslims fleeing sectarian violence in the Central African Republic, Save the Children said.
Three of the dead were said to be children, according to s pokesman Mike McCusker, who added that some survivors were left with horrific injuries.
He said doctors had described gory scenes after gunmen ambushed a convoy of refugees, firing a rocket-propelled grenade to halt the vehicles before attacking with firearms and machetes.
Mr McCusker told reporters: "Our doctor said there was blood everywhere, just pouring out of people like tap water."
The attack in the remote north-west of the country outside the town of Bouar illustrates how African and French peacekeepers are not reaching remote areas where violence goes unreported, the British charity's country director Robert Lankenau said.
Life remains precarious in the "still fraught and highly dangerous" situation, he added.
Mr McCusker said: "An incident of this magnitude has only come to the forefront because of our internal contacts at the hospital.
"Maybe a lot of these stories are not being reported."
The Central African Republic has a history of coups and dictatorship. More than 1,000 people have died since December alone and nearly one million have been forced from their homes since a rebel leader seized power last year.
Michel Djotodia stepped down a week ago as international criticism mounted over his inability to halt a wave of killings that some warn could explode into genocide.
A transitional national council is to vote Monday to choose a new interim president from among 24 candidates. But there are fears that whatever choice they make could further ignite violence that has pitted rival tribes and Christians against Muslims.
Mr McCusker said many lives were saved because Save the Children has been working at the hospital, providing drugs and other medical supplies, and local staff alerted them to Friday's carnage. Four surgeons quickly set up an operating room where they worked to save the most critically injured, including children.
He said he had difficulty getting news in Bangui, the capital, from doctors at the scene. "The (mobile) network is down, email isn't working, but somehow one of our doctors was able to make a Skype call," he said.