The ruling Congolese Labour Party of President Denis Sassou Nguesso won a large majority in run-off legislative elections last weekend, with 89 of the 136 seats, final results showed.
The PCT, which has been in power since 1997, had taken 57 of the 69 seats that were won outright in the July 15 first round, with another 10 going to its allies and just one to the opposition and another to an independent candidate.
In Sunday's second round it won another 32 of the 67 seats still up for grabs, Interior Minister Raymond Zephirin Mboulou said.
Independent candidates close to the PCT won 12 seats, against seven for the allied MCDDI party.
Overall the PCT and its allies took 117 seats.
The main opposition Pan-African Union for Social Democracy (UPADS) -- which held 11 seats in the outgoing legislature -- now has just seven deputies.
"Yesterday's vote witnessed the same fraud and irregularities that marked the previous round of voting," UPADS national secretary Martin Kimpo told AFP on Monday.
He accused the ruling Congolese Labour Party of robbing his party of as many seats as possible to prevent it from reaching the threshold for a parliamentary group.
"The regime will have a free hand to achieve its goal of amending the constitution in order to allow Denis Sassou Nguesso to run again in 2016," he said.
The electoral commission said Sunday it had to go through many incident reports and would release results within three days.
The mandate of the outgoing parliament ends at the end of the month and the new one is expected to hold its inaugural session in the first week of September.