Raila Odinga alleged on Thursday that dozens of Kenyans have been killed by the security forces and "nobody is talking about it".
The veteran opposition leader continues to dispute the legality of Kenyatta's rule and plans to have himself declared president at a ceremony on December 12, Kenya's independence day.
Odinga dismissed the USA pleas on Thursday. But the Supreme Court nullified the result, and a repeat election was held on October 26. "Up to today, no single ambassador has condemned the killing of people by police", he said. "Kenyan problems will be resolved by Kenyan people", he said.
NASA leaders made their way to the city mortuary on Thursday morning to mourn with the friends and relatives of fallen opposition supporters, whom they claim are victims of police brutality.
"Your county having passed the People's Assembly motion, the presidential inauguration team is requesting your office to provide a venue for this high level event in your county", the letters read in part.
The United States had urged opposition leaders to work within the law and avoid actions like the proposed "inauguration ceremony", a statement from the U.S. Embassy in Nairobi said on Wednesday, following a visit to Kenya by Donald Yamamoto, the acting assistant secretary of state for African affairs.
"The will of the people was expressed on August 8 and that is it".
Odinga and Kenyatta faced off in an election in August that Kenyatta won.
He alleges that IEBC allowed manipulation of figures during result transmission to give Mr Kenyatta an undeserved victory.
After the prayers, a total of 16 bodies were removed from the mortuary and ferried to various destinations for burial.
Each family was given Sh50,000 to help with burial arrangements.