PHNOM PENH (Reuters) - Cambodia dismissed on Thursday accusations by an anti-corruption pressure group that Prime Minister Hun Sen and his family have amassed $200 million in business interests including some with links to land grabs and environmental destruction.

The accusations, in a report by the group Global Witness, comes during a period of rising political tension between the veteran prime minister and the opposition hoping to challenge his grip on power in local elections in 2017 and a general election in 2018.

Global Witness, in its report titled "Hostile Takeover", said Hun Sen's family owns or partly controls companies with listed capital of more than $200 million.

That is likely to be a fraction of the real fortunes they hold through shell companies and the use of nominee owners, the group said.

Government spokesman Phay Siphan derided the report by a group that has been investigating issues such as illegal logging in Cambodia for decades.

"It has no quality," Phay Siphan said.

"It is just accusations. The report is personal propaganda against Hun Sen, the elected prime minister."

Global Witness said Hun Sen family companies had links to well-known global brands.

The family's interests were concentrated in the energy sector, and included fuel retail chains, power plants and renewable energy projects, the group said.

"Huge network of secret deal-making, corruption and cronyism" has helped prop up Cambodia's self-styled strongman, who has led the country for more than three decades, the group said. "The report should serve as a warning to foreign investors."

One of Hun Sen's sons rejected the allegations and suggested they were politically motivated.

"From my recent memory, whenever it is close to an election time, an organization called Global Witness has come up with very colorful accusations aimed at attacking the government and, in particular, making personal attack on my father," said the son, Hun Manet, in a Facebook post.

A senior member of the main opposition party, the Cambodia National Rescue Party, welcomed the airing of what he said were widely known details of the family's wealth.

"We all knew it but nobody could really talk about it," party member of parliament Son Chhay said.

"Now it is all public."

Recently, Hun Sen has come under pressure from the European Union to end what it sees as judicial harassment of opposition politicians. The EU has threatened to review about half a billion dollars in aid if the harassment continues.

Hun Sen has for decades dismissed accusation of rights abuses and links to graft, and regularly shrugs off Western pressure for reform while building strong ties with China.

China was the largest foreign investor in the fast-growing economy in 2015, accounting for $864 million of the $4.44 billion pledged.

(Reporting by Prak Chan Thul; Writing by Simon Webb; Editing by Robert Birsel)