International election observers in Guinea have voiced concern over "irregularities" during the first parliamentary poll since the 2008 coup.
A joint statement said "breaches" were observed in eight out of 38 constituencies.
The opposition coalition has already called for the 28 September vote to be annulled over "fraud".
Some provisional results have yet to be released by the electoral commission 11 days since the vote.
Most of the 38 directly elected seats in the 114-member parliament have been announced, but not the 76 chosen by proportional representation.
The National Independent Electoral Commission (Ceni) has admitted errors but defended the overall conduct of the vote.
The party of President Alpha Conde, the Rally of the Guinean People (RPG), is leading with 18 seats compared to 13 for the main opposition Union of Democratic Forces.
The BBC's Alhassan Sillah in the capital, Conakry, says tension have been mounting because of the delay in announcing the provisional results.
Many businesses and shops have been closed for more than a week fearing trouble and people are having difficulty buying essentials, our reporter says.
"Breaches and irregularities were observed in a certain number of constituencies, preventing a significant number of votes from being taken into account, and could therefore put into question the sincerity of certain results," the AFP news agency quotes the observers' statement as saying.
The observers include representatives from the UN, EU, West African block Ecowas and US and French diplomats.
Our correspondent says that six out of the eight constituencies in which the observers reported irregularities are opposition strongholds.
The observers urged Ceni to report these irregularities when it sent the provisional results to the Supreme Court, which must verify them.
But the opposition pulled out of the counting process and says it has no faith in the Supreme Court, whose head was appointed by the president.
The election is intended to replace a transitional parliament that has run the nation since military rule ended.
The run-up to the election was hit by violence, as well as ethnic and religious tension.
It has been much delayed and was supposed to be held six months after the 2010 presidential elections, which Mr Conde narrowly won.