Prabowo lost the July 9 election to Joko by more than eight million votes.
Hours before the election results were issued, Prabowo referred to the vote-counting as "a massive, structured and systematic fraud," and withdrew from the race after it became clear Joko was the winner, saying he would reject the results.
Prabowo plans to take his appeal to the Constitutional Court, which has the authority to order a vote recount or new election. It is, however, unlikely that the Court would rule in his favor. It has so far rejected all legal challenges to presidential election results since 2004.
Meanwhile, U.S. officials have congratulated Joko on winning the presidency. Secretary of State John Kerry applauded Indonesia's "commitment to democracy through free and fair elections." The White House said President Barack Obama spoke by phone with Widodo, telling him he "looks forward to meeting him at the earliest opportunity and to working with him to deepen the U.S.-Indonesia partnership..."