But it withdrew its protests on Friday after Kufuor called on all sides to respect the outcome of the election, and Afuko-Addo conceded defeat following Saturday's announcement.
"I acknowledge the electoral commissioner's declaration and congratulate Professor Mills," he said during a news conference at NPP's headquarters in the capital Accra.
Responding to complaints raised by both parties, Afari-Gyan said: "The commission did not find the evidence provided sufficient to invalidate the result".
Final results were reached by adding the votes garnered by each candidate in Tain to results from the other 229 constituencies that cast their second-round votes on Dec. 28, he said.
This is Ghana's fifth election - with stakes high as the country expects to start pumping oil in 2010 - since the return to multi-party democracy in 1992.