The party of Liberia's President George Weah, the Coalition for Democratic Change (CDC), has alleged that the opposition rigged last week's presidential run-off vote.
However, it has said that while it raised the issue it would not take the matter further as the party wanted to maintain unity in Liberia.
President Weah conceded on Friday evening once it was clear that his rival, Joseph Boakai, had a slim but unassailable lead.
The final results, released on Monday, showed that he won by just over 20,000 votes.
Local and international election observer groups, including from the regional bloc Ecowas and the European Union, all declared the polls free, fair, transparent and credible.
But CDC Secretary-General Jefferson Koijee told a news conference on Wednesday evening that his party had proof that the opposition interfered with the vote.
“We have empirical evidences that the elections were stolen," he said.
He took out a folder in which he said there were tally sheets from 21 counts that showed that there was ballot stuffing. Journalists were not able to see the evidence.
Mr Boakai's Unity Party has not yet responded to the allegations.
In his widely praised concession speech last week, Mr Weah said "the Liberian people have spoken and we have heard their voice" and that it was "a time for graciousness in defeat, a time to place our country above party, and patriotism above personal interest".
But he added that the CDC would remain a strong opposition. He is due to step down in January.
BBC