Congo's veteran leader Denis Sassou Nguesso has secured 67 percent of votes in his bid to extend his 32-year-old rule, partial results showed Tuesday, after a tense weekend poll.
The results covered 69 percent of the total electorate, the chief of the electoral commission Henri Bouka said, adding that they did not cover Pointe-Noire, the economic capital and opposition stronghold.
Oil- and timber-rich Congo has been on edge since an October constitutional referendum that ended a two-term limit on presidential mandates, allowing the 72-year-old former paratrooper colonel to run for office again.
The long-serving leader, accused by critics of rampant corruption and nepotism and of stifling democracy, was due to address a press conference later Tuesday.
Washington and the European Union meanwhile called for calm as communications lines were cut for a third day to prevent the opposition from publishing "illegal results" before the official announcement, according to authorities.
The streets of the capital Brazzaville were quieter than usual on Tuesday, as they were on Monday.
Five opposition candidates have urged people to "exercise their sovereignty" if Sassou Nguesso wins the election on the first round, as his supporters have said he will.
They created their own parallel "technical commission" to monitor the vote and compile information from polling stations to compare it to the official results.
By mid-day on Tuesday, mobile phone, internet and text services were still unavailable, according to AFP journalists in Brazzaville. A government source said they would be cut until after the official results were announced.
France expressed concern Tuesday over the cut in communication lines, urging "transparency" in the counting of votes.
"This vote took place in a worrying context, particularly due to the cut in communications. France is being vigilant and recalls its commitment to transparency and fairness in the electoral process," said foreign ministry spokesman Romain Nadal.
The European Union called on all sides to use legal routes to settle their differences and urged the authorities to open communication lines again.
The EU had earlier refused to send election observers, saying conditions had not been met for a transparent and democratic vote.
On Friday the UN called for calm, while Washington also urged the authorities to restore communications and "to complete the electoral process with accuracy, credibility, fairness, and transparency".
Congo recorded growth of five percent over the five years to 2014 but remains in dire straits with the vast majority of the population living in abject poverty.
Unemployment hit 34 percent in 2013, the last data available, and stood at 60 percent for 15 to 24-year-olds. The IMF fears "domestic instability" without progress in the battle to eliminate poverty.
Sassou Nguesso served as president from 1979 to 1992 and returned to power in 1997 following a civil war. He won two successive mandates in 2002 and 2009, but both tallies were contested by opposition parties.