Cambodia's newly returned opposition leader has denounced political intimidation and warned that this month's election will be a "sham" unless he is allowed to stand as a candidate.
Sam Rainsy, who was greeted by huge crowds on Friday after his return from self-imposed exile in France, is seen as the main challenger to strongman Prime Minister Hun Sen.
But he has been removed from the electoral register and is unable to run as a candidate in the July 28 polls unless parliament amends the law.
In an interview with Radio Free Asia, Rainsy warned that demonstrations might break out if he is not allowed to stand.
"If I can't participate, after the elections all the Cambodian people will protest and the whole international community will condemn the result and regard this as a sham election," Rainsy was quoted as saying.
"Then we will demand a real election to allow Cambodians to decide their true destiny," he added.
US lawmakers have called for the United States to cut off aid to Cambodia unless the vote is free.
Rainsy, a French-educated former banker, fled in 2009 to avoid charges he contends were politically motivated.
He was convicted in his absence of charges including inciting racial discrimination and spreading disinformation and had faced 11 years in jail but received a royal pardon earlier this month.
Aiming to finally unseat Hun Sen, he recently joined with former rival and veteran activist-turned-politician Kem Sokha to form the CNRP.
Although he is not a candidate, he has hit the campaign trail to spearhead his party's efforts to end Hun Sen's nearly three decades in power.
The UN's special rapporteur on human rights in Cambodia, Surya Subedi, last week urged Cambodia to let Rainsy play a "full part" in politics.
Hun Sen is one of Southeast Asia's longest-serving leaders. His Cambodian People's Party (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.
The opposition also accused people in power of being behind an attack by an unknown gunman who fired a bullet at the party's headquarters in the early hours of Saturday.
Nobody was hurt in the incident at the offices of the Cambodia National Rescue Party (CNRP) in Phnom Penh which was closed at the time.
"I think this attack was orchestrated by people in power. This is a politically motivated case," CNRP spokesman Yim Sovann told AFP.
"This is a cowardly act.... We're not scared by this attack at all," he said.
National police spokesman Kirt Chantharith confirmed the attack by the unidentified gunman and said police had collected a bullet.
"We are investigating the case," he told AFP.