Hun Sen, Cambodia's leader for 28 years, has a reputation of dealing harshly with his opponents.
Sam Rainsy said earlier Thursday that he plans to hold training sessions and rehearsals to show supporters how to hold peaceful protests, since the Cambodian people have little experience with opposition rallies. He said he would call in foreign experts to help with the training.
"We are in the learning process," Sam Rainsy told reporters. "We are receiving training and advice from people all over the world who want to help ensure that demonstrations in Cambodia will be peaceful. We will conduct rehearsals. We will assemble people and train them in how to resist violence."
He denied allegations by the Interior Ministry, which recently set a letter to all foreign embassies accusing the opposition of trying to topple the government.
"We have no plan to topple anyone," Sam Rainsy said. "We are protesting the election results and the election conduct and a lack of transparency. We want to bring justice to the voters."
In its statement, the ruling party did not address the opposition's demand for an impartial investigation into the election. But it urged the opposition to hold another round of talks to ease the standoff, rather than taking its discontent into the streets. The two sides have already held three meetings over the dispute.
The protest is planned for one day before the National Election Committee is expected to ratify the results.
"The announcement by the Cambodia National Rescue Party to hold a massive demonstration against the result of the election before the final result is announced will affect the livelihood of the people who are living peacefully," the ruling party said in its statement.
Hun Sen's party also denounced the planned protest as an effort to "intentionally destroy the election results" and a violation of Cambodia's spirit of national reconciliation. It repeated its claim that the election was free and fair.
The opposition's main complaint alleges that the voter registration process failed to properly list possibly more than 1 million people, who were therefore unable to vote. Several nonpartisan poll-watching groups support that claim.