Incumbent President Filip Vujanovic (left in photo) said he won 51.3 percent of the votes, with Miodrag Lekic, a former ambassador and the opposition's unity candidate, holding 48.7 percent. The Democratic Front gave the race to Lekic, however, 50.5 percent to 49.5 percent, with over 90 percent of votes counted.

State election authorities have yet to release any official results.

Still, the incumbent sounded confident: "I want to declare victory that we have achieved," Vujanovic told his supporters in the capital, Podgorica.

An inconclusive vote could increase instability in Montenegro, which opened EU accession talks in 2012, pending reforms. The presidency holds little power, but such a tight result deals a blow to Montenegro's governing coalition, which has ruled the country virtually unchallenged since the break-up of the former Yugoslavia.

"The citizens of Montenegro have trusted me to become the president," Lekic said. "I urge the other side to act in a serious and responsible manner. We will demand that each ballot be counted."

Though a final number on voter participation is not yet in, the country's DIK election commission estimated a turnout of roughly 60 percent among Montenegro's 512,000 eligible voters - from a population of about 630,000. This is slightly higher than was predicted before the vote, but lower than in previous polls.

mkg/msh (AFP, Reuters, dpa, AP)