BANGUI, Central African Republic - Assailants armed with heavy weapons attempted late Thursday to attack the presidential palace as well as the residence of the Central African Republic's embattled leader, but were pushed back, officials said.

Reached by telephone, Guy Simplice, spokesman for President Michel Djotodia, said there had been heavy fighting near the seat of government before the army was able to block the aggressors. Although the attackers could not immediately be identified, for weeks there have been rumors that a Christian militia, believed to be backed by the president, who was ousted by Djotodia in a coup nine months ago, would attempt to seize back power.

The heavy arms fire could be heard from the five-star Hotel Ledger, near the town center, where international journalists are staying. A rocket came over a wall, landing on the hotel grounds.

The events are only the latest indicating that this deeply poor, but until recently relatively stable nation, is tipping into anarchy. Earlier Thursday, international forces were sent to pick up truckloads of decomposing bodies of slain Muslims, whose remains had been left at a mosque by their friends and relatives, who were too frightened to be seen burying them in a city where Christian-on-Muslim and Muslim-on-Christian attacks have become a daily occurrence.

It also comes a day after the African Union lost six peacekeepers, who were attacked in the Gobongo neighborhood of the capital. Their destroyed car, with at least one body inside, had not been removed a day later, underscoring how dangerous this chaotic country has become, even for the international forces tasked with pacifying it, said African Union spokesman Eloi Yao.

As the African Union was struggling to secure that crime scene, they discovered another: a mass grave close to the presidential palace.

"We found around 20 bodies in a state of decomposition in an area that we call Panthers' Hill," Yao said.

U.N. Secretary-General Ban Ki-moon said he was appalled by the violence, including reports Thursday of dozens more bodies found, and called on the transitional authorities "to rein in those fomenting and perpetrating the violence," spokesman Martin Nesirky said.

The U.N. chief welcomed appeals for peace by Christian and Muslim leaders, reiterated that those responsible for atrocities must be held accountable, and expressed sadness at the deaths of the six peacekeepers and a U.N. national staff member, Nesirky said.