Coalition of Patriots for Change says a 72-hour unilateral truce will be observed across the Central African Republic.
One peacekeeper was killed in an ambush by rebels near the town of Grimari in the Central African Republic (CAR), as deadly violence continues after a disputed election last month.
Two other soldiers were wounded when fighters from a coalition of rebel groups carried out two ambushes on peacekeepers from Burundi and Bangladesh, the United Nations Mission in the country, MINUSCA, said in a statement.
The peacekeepers were carrying out a security operation around Grimari, 200km (120 miles) northeast of the capital, Bangui, it added.
The Burundian peacekeeper was killed in the second ambush, and two Bangladeshi peacekeepers were wounded during the attacks and receiving treatment.
UN Secretary-General Antonio Guterres warned the attacks “may constitute a war crime” and called for the perpetrators to be brought to justice, UN spokesman Stephane Dujarric said.
The UN chief also reiterated “his deep concern over the continued destabilisation efforts by armed groups throughout the country”, and called on all parties ”immediately to stop the violence and resolve their differences through peaceful means”.
The rebels are protesting against the re-election on December 27 of President Faustin-Archange Touadera. Following the January 4 announcement of Touadera’s victory, the rebel coalition threatened to take the capital. They also seized towns in other parts of the country before the vote.
The army is supported in its battle against the rebels by forces from Rwanda, Russia, France and the UN.
On Wednesday, security forces repelled attacks by rebels trying to seize Bangui after intense fighting on the city’s outskirts in a major escalation of violence that has rocked the country since last month.
At least one Rwandan peacekeeper was killed and another wounded, according to the UN, while the CAR’s Prime Minister Firmin Ngrebada said at least 30 rebels also died.
Al Jazeera’s Malcolm Webb, reporting from Bangui, said the situation was “tense” ahead of the expiration on Sunday evening of a 48-hour ultimatum given by the coalition of armed groups to the government.
“Security sources say they also now have several cells here within the city in preparation for an attack,” Webb said.
“This comes ahead of a constitutional court ruling that’s due on Tuesday which will potentially reaffirm the office of President Touadera, bringing him in for a second term.”
A sharp increase in violence in the past few weeks has forced more than 60,000 people to flee the country, seeking refuge in Cameroon, the Democratic Republic of the Congo (DRC), and other neighbouring countries, the UN’s refugee agency (UNHCR) said.
“The UN has reported widespread rights abuses – kidnappings, tortures, killings of civilians – and that’s caused many people to flee their homes,” Webb said. “People are still on the move; many aren’t risking it to see what’s going to go down.”
The DRC has received the highest number of refugees – about 50,000 since December, which includes 10,000 who arrived on Wednesday when the rebel coalition staged attacks on the outskirts of the capital, according to UNHCR.
However, Cameroon has also seen an increase in the number of families, especially women and children, coming from Central African Republic, it added.
“In the beginning when they came in, they said it was a preventive movement, they were afraid because they remembered the violence that they experienced in 2013,” said Helen Ngoh Ada, UNHCR spokeswoman.
“Lately, those who have been coming in have been saying that they came traumatised basically, and they experienced some form of abuse, human rights violations, and that’s why they fled,” she said in an interview with The Associated Press news agency.
People are allowed to cross from the CAR to Cameroon, but the borders are closed for traders and trucks and supplies have not entered into Central African Republic for several days, said Ngoh Ada.
“It means that the livelihoods of people in the Central African Republic are threatened, and that will be one of the reasons why people would be crossing over into Cameroon,” she added.
Mineral-rich CAR has faced deadly inter-religious and inter-communal fighting since 2013, when predominantly Muslim Seleka rebels seized power from former president Francois Bozize after long claiming marginalisation.
Resistance to Seleka rule eventually led to Muslims being targeted en masse, with some beaten to death, mosques destroyed and tens of thousands forced from the capital in 2014.
Bozize has been blamed for inflaming the violence in the last weeks, which erupted after the constitutional court rejected his candidacy in December.