Cambodia's Prime Minister Hun Sen and his family have built a multi-million-dollar business empire spanning the impoverished country's most lucrative sectors, a watchdog said Thursday, warning foreign investors against bankrolling his regime.

Hun Sen, a former army commander who defected from the Khmer Rouge, has dominated Cambodia's political scene during a 31-year reign marred by accusations of corruption, electoral fraud and rampant rights abuses.

During that time the wily premier has also used his position to hand control of swaths of the country's economy to his family, the UK-based watchdog Global Witness detailed in a report Thursday. 

Hun Sen and his relatives have amassed more than $200 million through their interests in 114 private companies, according to the report, which cited data from the country's Ministry of Commerce.

The family's firms span Cambodia's trade, finance, energy and media industries, with business links to major global brands such as Visa, Apple and Honda, the report said. 

"Behind the scenes of Hun Sen's dictatorial reign, his family is amassing vast personal fortunes," the watchdog said, describing a "huge network of secret deal-making, corruption and cronyism which is helping secure the prime minister’s political fortress". 

The premier's eldest daughter Hun Mana, a media mogul, has the biggest portfolio in the family with interests in 22 companies, 18 of which list her as chair or director, the report added.

She slammed the report in a Facebook post Thursday, calling it full of lies and an "attack" on her family.

Government spokesman Phay Siphan also dismissed the report as an effort to discredit the premier.

"The report intends to break the Cambodian people's respect for the Prime Minister," he told AFP.

"We are not paying attention to it," he added.

But Patrick Alley, the founder of Global Witness, described Hun Sen's family as having an "almost feudal control of the economy" and urged foreign investors to reassess their stakes. 

"Foreign investors can and should opt out of bankrolling a regime that kills, intimidates or locks up its critics," he told AFP. 
Hun Sen has faced fierce criticism from rights groups in recent months, who accuse him of clamping down on rivals and critics as he eyes elections in 2018. 

The European Parliament recently threatened to review nearly $500 million of aid if his government continues to repress opponents, prompting a rebuke from Hun Sen who warned against interference in domestic politics.

Transparency International ranks Cambodia as one of the most graft-riddled countries in the world, and the most corrupt in Southeast Asia.