BANGUI, Central African Republic — Secretary of State John Kerry Friday called for an immediate end to violence in the Central African Republic, where clashes this week left “dozens” of people dead including six African Union peace-keepers.

A mass grave containing at least 20 bodies was discovered Thursday in the capital, Bangui, Kerry said in a statement emailed by the State Department. The bodies of 44 people were found in the streets of the city Thursday after clashes on Dec. 24 and Dec. 25, Romaric Bekourou, a spokesman for the Red Cross, said by phone. Sixty people were injured, he said.

“The U.S. calls on the CAR transitional authorities to immediately end the violence, end the use of torture, and investigate and prosecute all those implicated in grave human- rights abuses,” Kerry said.

Central African Republic has descended into lawlessness since March, when an alliance of rebel groups known as Seleka overthrew former President Francois Bozize.

At least 1,000 people have died in the conflict, according to Amnesty International. The violence has forced 710,000 people to flee their homes and another 75,000 have gone into exile, according to the United Nations Refugee Agency.

Central African Republic is the world’s 12th-biggest producer of rough diamonds by volume, according to the U.S. Geological Survey.

The gems, along with timber exports, are the largest source of foreign exchange for the $3.6 billion economy. The country also produces oil and has deposits of uranium, the USGS says on its website.

Suspected self defense militias, known as anti-Balakas, attacked the presidential palace in Bangui last night, Guy Simplice Kodegue, spokesman for President Michel Djotodia, said in a phone interview. Gunfire erupted at about 9 p.m. local time and continued for about 30 minutes, he said.

“Fierce fighting took place around the palace, but the attackers were repelled by the presidential guard,” Kodegue said. “All is quiet at the moment.”

An African Union-led International Support Mission to the Central African Republic, known as Misca, is deploying 3,600 multinational troops in the country, while France, the nation’s former colonial ruler, has sent 1,600 soldiers to help stabilize the country.

Unidentified gunmen attacked a Chadian contingent of Misca who were on patrol on Christmas Day, killing six of them and wounding five more, the African Union said in a statement on its website.

The discovery of the mass grave Thursday comes after 30 bodies were found behind Bangui’s main water complex on Dec. 24. State Prosecutor Ghislain Gresenguet announced on national radio that an investigation has been opened into the deaths.

U.N. Secretary-General Ban Ki-moon is “appalled” by the continuing violence, according to a statement emailed by his spokesman Friday. A U.N. national staff member was killed in the country on Dec. 24, he said, without providing further details.