PHNOM PENH — Cambodia's Prime Minister Hun Sen vowed on Wednesday to stay in office for another decade following the dramatic arrest of the country's main opposition leader for treason.

Hun Sen, 65, has held power for 32 years, making him one of the world's longest-serving leaders.

But he faces a key test at national polls in 2018 with the main opposition party gaining in popularity as anger mounts over corruption, inequality and rights abuses.

His opponents, as well as NGOs and the critical press, have increasingly been smothered by court cases and threats in recent months while Hun Sen has vowed violence if he loses power.

On Tuesday the country's most prominent opposition leader Kem Sokha was charged with treason for allegedly conspiring with unnamed foreigners to topple the government.

Hun Sen has accused the United States of being behind the plot.

In a characteristically bombastic speech on Wednesday, he spoke at length about the alleged treason plot and said he had no intention of leaving politics any time soon.

"After seeing the painful event of treason committed by Khmer nationals who have been arrested — and there may be more arrests — I have decided to continue my work for at least 10 years more," he said during a speech to more than 10,000 garment workers in Phnom Penh.

"Please foreigners, don't be jealous with me, I am the longest serving prime minister in the world," he added.

That latter boast is incorrect. Seven leaders, mostly in Africa, have been in power longer than Hun Sen.

The Cambodian strongman has dramatically escalated his rhetoric against Washington in recent years, accusing the US of trying to instigate "color revolutions" to end his rule.

Washington has a complex relationship with Cambodia, secretly bombing it during the Vietnam War and then becoming one of its biggest donors as it rebuilt from the ashes of the brutal Khmer Rouge era.

Kem Sokha's arrest was sparked by a speech he gave to Cambodians in Australia in 2013 in which he claimed to have support from academics in the US and Canada to defeat Hun Sen.

His Cambodia National Rescue Party had been widely tipped to perform strongly in the 2018 polls, buoyed by the youth vote in a country where many are tired of Hun Sen's rule.

But the strongman retains significant support through his party and a government bureaucracy that has known no other leader for three decades.

Supporters say Hun Sen has brought stability and economic growth to a desperately poor country battered by civil war and a genocide that killed up to a quarter of the population.

Crackdowns on opposition politicians by the premier are routine before elections but the recent series of charges is unprecedented. — AFP