WASHINGTON/PHNOM PENH (Reuters) - The United States said on Wednesday it would restrict entry to people involved in the Cambodian government’s actions to undermine democracy, including the dissolution of the main opposition party and imprisonment of its leader.

The visa sanctions were the toughest steps by any Western country since a crackdown on critics of Prime Minister Hun Sen ahead of an election next year in which the authoritarian leader seeks to extend more than three decades in power.

“We call on the Cambodian government to reverse course by reinstating the political opposition, releasing Kem Sokha, and allowing civil society and media to resume their constitutionally protected activities,” the State Department said in a statement.

“The secretary of state will restrict entry into the United States of those individuals involved in undermining democracy in Cambodia. In certain circumstances, family members of those individuals will also be subject to visa restrictions,” it added.

Cambodia’s Supreme Court dissolved the main opposition party, the Cambodia National Rescue Party (CNRP), last month at the government’s request.

Kem Sokha was arrested for allegedly plotting to overthrow the government with U.S. help. He has rejected the accusation as a political ploy.

The dissolution of the CNRP has been condemned by some Western countries as the most serious blow to democracy since an international peace deal and U.N.-run elections in the early 1990s ended decades of war and genocide.

Cambodia’s government condemned the visa restrictions announced by Washington.

“This statement shows that the United States is destroying democracy,” government spokesman Phay Siphan told Reuters, saying that the actions against the opposition had been legal and took place through the courts and parliament.

“The CNRP are not politicians, they are rebels and terrorists,” he said.

The United States said after the banning of the CNRP that the election “will not be legitimate, free or fair,” and withdrew an offer to help fund it.

The European Union has raised the possibility of withdrawing trade preferences which are vital for the garment industry that accounted for well over 60 percent of Cambodia’s exports last year.

Hun Sen has dismissed Western pressure and built closer ties to China, while opposing U.S. efforts to rally Southeast Asian countries to stand up to Beijing’s expanding power in the region.

Earlier on Wednesday, Hun Sen accused Sam Rainsy, who stepped down as CNRP leader earlier this year in a bid to forestall a ban on the party, of committing treason by inciting soldiers to defy orders.

Hun Sen said Rainsy, who lives in exile in France, would face new legal action over the comments.