The latest upsurge in deadly violence in the Central African Republic saw the first use of heavy weapons and more sophisticated military tactics by a predominantly Christian armed group, a senior U.N. official said Thursday.

Diane Corner, the U.N. deputy special representative in the beleaguered country, said that since May 8 more than 150 people, including six U.N. peacekeepers, have been killed in the southeastern city of Bangassou, the southern town of Alindao and the northern town of Bria — and the death toll may rise.

Over 25,000 people are displaced in the three localities and 3,000 people from Bangassou have fled across the border to northern Congo, which has seen a recent outbreak of Ebola cases, she said in a video press conference with U.N. reporters.

Corner said the fighting is "more complex" than a renewal of sectarian violence between Christians and Muslims that has plagued the country since late 2013.

"There are many on both sides within the Christian and Muslim community who are continuing very strongly to work for peace and are doing all they can to prevent the situation from worsening," she said.

Corner said there are 14 armed groups in the country, "some intent on wreaking havoc."

The broader conflict is due to a number of issues, she said. The regions are concerned the government in the capital of Bangui has forgotten them. The seasonal movement of cattle herders can provoke conflicts. There is competition for control of resources, including diamonds and gold and a large trade in coffee and cattle.

In Bangassou, which was previously calm and had good inter-communal relations, Corner said a large group of mainly Christian rebels known as the anti-Balaka surrounded a group of U.N. peacekeepers that led to five deaths.

They then reinforced their ranks and attacked the city, she said. Anti-Balaka fighters pinned down peacekeepers at the U.N. base and then launched an attack on civilians, particularly the Muslim population.

The U.N. got reinforcements through but their arrival was hampered by new tactics the rebels used including putting trees across the road and burning bridges, she said.

"This is the first time we have seen a major outbreak of this scale," Corner said.

She said the anti-Balaka used heavy weapons that the U.N. had not seen before, including mortars and grenade launchers. "It looks as if someone has been financing" the new weapons and the money likely came from within the country, she said.

The death toll of 115 in Bangassou may rise, Corner said, and while the situation is returning to calm and U.N. peacekeepers are gradually regaining control "the situation remains extremely fragile," with 7,200 displaced people in the city.

Corner said Cardinal Dieudonne Nzapalainga of Bangui has been in Bangassou the last few days "and has been leading efforts to try to calm the situation."

In addition to the fears sparked by the anti-Balaka attack on Muslims, she said there are other tensions in the city between rival ethnic groups that don't necessarily follow religious lines. While it was an anti-Balaka group that attacked, the national anti-Balaka coordination office condemned the attack and the "major portion" of anti-Balaka have said they remain committed to disarmament, she said.

In Alindao, the U.N. has reports that anti-Balaka fighters clashed with a group of ex-Seleka mostly Muslim rebels on May 9, leaving 11 fighters dead, she said. The U.N. knowns of 38 casualties though some reports allege a much higher death toll, she said.

Corner said about 8,500 people have been displaced and have sought refuge at a Roman Catholic mission.

In Bria, she said, two wings of the anti-Balaka coalition engaged in minor clashes starting May 14 that escalated to "a much larger explosion" which left dead and injured. Ten thousand displaced people were already gathered around the U.N. base in the town, and the latest clashes forced an additional 5,000 people to flee and seek refuge there, she said.

"We are engaging with civil society leaders, with religious leaders, to seek to calm the situation," Corner said.