PHNOM PENH (Reuters) - Cambodia ordered the U.S.-funded National Democratic Institute to stop activities and remove foreign staff on Wednesday in the latest move by Prime Minister Hun Sen’s government against American interests ahead of elections next year.

FILE PHOTO: Cambodia's Prime Minister and president of Cambodian People's Party (CPP) Hun Sen speaks during a campaign rally in Phnom Penh, Cambodia June 2, 2017. REUTERS/Samrang Pring

The U.S. State Department said it was “deeply concerned” by the deterioration in Cambodia’s democratic climate in recent weeks, including the order against the pro-democracy group and a threat to close a newspaper founded by an American journalist.

Growing anti-Western sentiment from Hun Sen comes amid increasing tension ahead of next year’s elections, in which he is expected to try to extend his more than three decades in power.

Cambodia’s foreign ministry accused the NDI of operating without a registration and said foreign staff had seven days to leave. Authorities were “geared up to take the same measures” against other foreign NGOs which fail to comply with the law, the ministry added.

The NDI says it works with political parties, governments and civic groups to “establish and strengthen democratic institutions.” It did not respond to a request for comment.

The U.S. embassy described the group as impartial and said it had been working in Cambodia since 1992 with major parties including the ruling Cambodian People’s Party.

At a regular news briefing in Washington, U.S. State Department spokeswoman Heather Nauert said recent Cambodian government actions curtailing freedom of the press and civil society were “troubling.”

As well the NDI order, she highlighted the reported closure of Cambodia’s only opposition-aligned radio station and tax investigations into independent media outlets and NGOs.

Naeurt said Secretary of State Rex Tillerson and U.S. Ambassador William Heidt had discussed U.S. concerns with Cambodian leaders in recent weeks and months.

Hun Sen, a former Khmer Rouge guerrilla who is now one of China’s closest allies, has ratcheted up steps against the United States this year from ending joint military exercises to demanding forgiveness of war-era debt from the 1970s.

He also lashed out at non-governmental organizations and accused them of funding groups attempting to overthrow his government.

On Tuesday, Hun Sen ordered the Cambodia Daily, an English-language newspaper founded by an American, to pay taxes accrued over the past decade or face closure.

Nauert called the demand for $6 million in taxes from the newspaper, along with other levies imposed against the press, “exorbitant” and said Heidt had spoken to the head of tax agency about the matter.

The opposition has accused Hun Sen and his party of a crackdown on critics and last week a U.N. human rights envoy said Cambodia “appeared to be approaching a precipice”.