Angola demanded an apology from the United Nations on Saturday after the world body called for an investigation into the killing of members of a Christian sect by police last month.
Details of an April 16 police raid in the remote hills of central Huambo province have been fiercely contested, with authorities saying 13 sect members were killed, while opposition party UNITA claims over 1,000 civilians were slain in the operation.
U.N. High Commissioner for Human Rights (UNHCR) spokesman Rupert Colville has urged Angola to ensure "a truly meaningful, independent, thorough investigation" into the alleged massacre.
The government responded angrily, accusing the U.N. of violating its own procedures and asking for a retraction and an official apology.
Authorities say the 13 were killed only after members of the Seventh Day Adventist breakaway group, known as "Light of the World", had killed 9 police officers by sniper fire.
"We find it difficult to believe that they have killed and buried more than 1,000 people during the night, without leaving traces," a government statement said.
However, UNITA and human rights activists have contested the government's version, accusing police of murdering more 1,000 civilians as punishment during the siege aimed at crushing a group that defied the government.
Sect leader Jose Kalupeteka, a popular anti-authority preacher who says the world will end on Dec. 31, is in police custody after he was captured in a separate raid on a UNITA stronghold.
Oil-rich Angola, led by President Jose Eduardo dos Santos for the past 36 years, said its attorney general was investigating the incident.
The violence has drawn rare attention to OPEC member Angola's well-funded security forces, which were funded to the tune of $6.5 billion in 2013, which was the biggest slice of the annual budget and more than any other sub-Saharan country.