What you need to know:
- Fayulu said the DRC's Independent National Election Commission (CENI) had "quite simply fabricated the results it published".
- He suggested setting up an AU special committee to verify the results.
The runner-up in DR Congo's controversial presidential election has proposed staging the poll again within six months.
In a letter to the African Union summit in Addis Ababa, Martin Fayulu restated his allegation that the vote result had been rigged, and suggested "holding the elections again within six months".
Felix Tshisekedi was declared winner of the December 30 ballot with 38.5 percent of the vote, against Mr Fayulu's 34.8 percent.
Mr Fayulu, whose letter was made public on Monday, said the DRC's Independent National Election Commission (CENI) had "quite simply fabricated the results it published".
He pointed to reports from independent election monitors and observers from his own coalition, Lamuka, as well as to vote tallies by the CENI itself that have been leaked to the press.
"(All) attest that I was elected president of the Democratic Republic of Congo with more than 60 percent of the vote," he charged.
Mr Fayulu suggested setting up an AU special committee to verify the results.
The two-day AU summit, which was winding up on Monday, was attended by President Tshisekedi, who was elected the organisation's second vice president for 2019.
He also met UN Secretary General Antonio Guterres and the European Union's foreign relations chief, Federica Mogherini.
Mr Fayulu's bitterness over the election outcome has mingled with relief outside the country that the vote was calm by DRC standards and led to the country's first-ever peaceful transition of power.
Mr Tshisekedi succeeded Joseph Kabila, whose 18-year tenure was criticised for authoritarianism, rights abuses and corruption.
Both Mr Fayulu and Mr Tshisekedi are from the ranks of the opposition.
The election should have taken place at the end of 2016 but Mr Kabila stayed in office for an additional two years, invoking a caretaker clause in the constitution.