Cambodian opposition leader Sam Rainsy lost his bid to regain lawmaker status Thursday in a new setback to his efforts to challenge strongman premier Hun Sen in this weekend's election.
Rainsy returned to Cambodia last week after receiving a surprise royal pardon for criminal convictions he contends were politically motivated.
But he is barred from running as a parliamentary candidate as the authorities said it was too late to add his name to the electoral register.
Rainsy turned to the ruling party-dominated National Assembly Tuesday in an attempt to regain his seat -- a move he had hoped would make him eligible to vote and also stand for election.
Heng Samrin, the president of the parliament, told Rainsy in a letter Thursday his request was denied because he had left his party to form the new Cambodia National Rescue Party (CNRP), which has no seats in the assembly.
"This is a politically motivated case and the (ruling) Cambodian People's Party is scared by Sam Rainsy's popularity," CNRP spokesman Yim Sovann told AFP.
"This clearly shows that the election is not going to be free and fair," he said, adding that the opposition would try all possible ways to enable Rainsy to participate in the polls.
Rainsy has also asked the country's Constitutional Council to reinstate him as a voter and a candidate, but the body has not yet responded to his request, Yim Sovann said.
Rainsy, seen as the only major challenger to Hun Sen, returned to Cambodia on Friday from France where he had lived in self-imposed exile after fleeing in 2009.
The 64-year-old had faced a total of 11 years in jail but was pardoned by King Sihamoni earlier this month at Hun Sen's request.
Rainsy was stripped of his parliamentary seat in 2011 and removed from the electoral register late last year.
Last month all 28 opposition MPs were stripped of their status by a committee made up of ruling party members which accused them of violating parliament's internal rules by joining forces to form a new party.
They are still allowed to participate in Sunday's election.
Hun Sen is one of Southeast Asia's longest-serving leaders. His CPP won the last two polls by a landslide amid allegations of fraud and election irregularities.
His government is regularly accused of suppressing political freedoms and muzzling activists. In May Hun Sen said he would try to stay in power for another decade.