PHNOM PENH (Reuters) – An outspoken deputy of Cambodia’s detained opposition leader fled the country on Tuesday, saying she feared for her safety after Prime Minister Hun Sen threatened further arrests of opposition politicians.

Kem Sokha, leader of the opposition Cambodia National Rescue Party (CNRP), was arrested on Sept. 3 and charged with treason in a widening crackdown on critics of Hun Sen, which his opponents say is a ploy to win a general election next year.

The situation in Cambodia was “very dangerous for CNRP leaders”, Mu Sochua, 63, told Reuters via messages on social media site Facebook, adding that she had heeded the prime minister’s threat.

Government spokesman Phay Siphan said Mu Sochua had “left of her own choice” and he did not know whether authorities had planned to arrest her.

Known internationally for campaigns to fight sex trafficking and assert women’s rights, Mu Sochua had been among the most vocal opposition politicians in Cambodia since Kem Sokha was arrested and accused of plotting to take power with U.S. help.

She told Reuters last week that around half the CNRP’s members of parliament had fled the country in fear.

Hun Sen, who has ruled for more than three decades, threatened more arrests of opposition politicians on Monday, attacking them as “rebels in the city” bent on staging a “color revolution” despite past failures.

Western countries have condemned the arrest of Kem Sokha, but China has voiced support for the government of Hun Sen, 65. He is a former commander in the Khmer Rouge who later defected from the group whose genocide devastated Cambodia in the 1970s.

Strong gains by the CNRP at local council elections in June had pointed to a tough battle for Hun Sen in next year’s general election. Despite years of annual economic growth of around 7 percent, popular anger has grown over inequality and accusations of cronyism.

In his first comments since his arrest, Kem Sokha said in a Facebook posting on Monday that he was seeking positive change in Cambodia through the ballot box and not through revolution as charged. One of his three deputies remains in Cambodia.