The worst violence to hit Central African Republic's capital in a year further deteriorated Monday as more than 500 inmates escaped from a prison and militia fighters looted the offices of international aid organizations, officials said. The death toll from several days of clashes reached 42 including a teenage boy who was decapitated.

The unrest erupted as transitional President Catherine Samba-Panza was in New York at the U.N. General Assembly, sparked by the death of a Muslim man whose body was left near a mosque. Muslim militants then attacked a Christian neighborhood with weekend clashes leaving several dozen people dead.

Amnesty International, which has documented the human rights abuses since the conflict first erupted in early 2013 with the overthrow of the president of a decade, said the latest fighting had shattered the peace in Central African Republic. Sectarian violence had ebbed in recent months with the arrival of a U.N. peacekeeping force and after tens of thousands of Muslims fled the country for their lives.

"The deadly violence in the capital illustrates that CAR remains in a very fragile state and that immediate action must be taken to enhance the capacity of U.N. peacekeepers to detect and respond effectively to such incidents before escalation of attacks on civilians," said Alioune Tine, Amnesty International regional director for West and Central Africa.

The United States swiftly condemned the unrest, and pledged its support for Samba-Panza's government, which was supposed to organize elections by year-end. Few see the Oct. 18 dates as possible, and the near-anarchic conditions in Bangui on Monday further cast doubt on their feasibility. Pope Francis is also due to visit in late November as part of his upcoming Africa trip.

"We fully support the efforts of the Central African and international forces to re-establish order and bring these perpetrators to justice," U.S. State Department spokesman John Kirby said in a statement. "The era during which such individuals have been able to carry out their malevolent actions with impunity must come to an end."

Monday's jailbreak, though, at Nagaragba unleashed at least 60 high-level convicts including militants from both the Muslim ex-Seleka rebellion and the Christian anti-Balaka fighters, authorities said. The escape was confirmed by head clerk Thierry Ngoalessio at Bangui's court, as well as witnesses who saw the men fleeing.

Earlier in the day, a group of protesters had gathered in downtown Bangui in an effort to march on the presidential palace. At least six people died when the group was fired upon and protesters blamed peacekeepers for shooting into the crowd to disperse the demonstration, said Christophe Gazam-Betty, a former communications minister.

However, the U.N. mission known as MINUSCA denied that its peacekeepers were to blame for the shooting deaths in this heavily-armed city.

"MINUSCA protected the presidency but did not kill protesters," said Myriam Dessables, a spokeswoman for the mission, told The Associated Press by telephone.

And a spokesman for the peacekeeping office at U.N. headquarters, Nick Birnback, said, "MINUSCA is patrolling and doing everything it can to stabilize the situation."

Among the 42 victims in recent days were three teenage boys, one of whom was decapitated, according to the U.N. children's agency citing preliminary reports from local organizations.