Prime Minister Hun Sen intensified his attacks on the US yesterday, lambasting its failed attempts at regime change across the world, with one observer noting the recent, and fervent, anti-US nationalism could see relations with the superpower deteriorate to the point of provoking congressional action.

While Hun Sen has long been known to deploy anti-US rhetoric, in recent days it has appeared to reach a climax, with the premier levelling direct accusations that the United States conspired with the opposition to topple his government.

The surprise midnight arrest of Cambodia National Rescue Party President Kem Sokha on Sunday for alleged treason was predicated on a 2013 video in which he spoke of getting US assistance to plan his political career. The re-emergence of the video came after unsubstantiated conspiracy theories began appearing on an anonymous Facebook page – and soon after, government mouthpiece Fresh News – accusing Sokha, his family, freelance journalists, foreign NGOs, the CIA and the “extremist” ruling party of Taiwan of orchestrating regime change in Cambodia.

Following Sokha’s arrest, Hun Sen quickly jumped to accuse the US of plotting a coup, evoking the US-backed Lon Nol regime that ousted then-King Norodom Sihanouk in 1970. Yesterday, he continued the attack, questioning the US’s foreign policy initiatives in Syria, Libya and Iraq, where US-supported movements to remove authoritarian governments ended up leaving those countries worse off, and specifically calling out the US for its backing of rebel groups in Syria. “The damage there has led to a situation where three groups – the government, groups supported by the US and ISIS – now control the country.”

He went on to say any statements in support of Sokha were an attempt to protect the “puppet”, and that the government would look into groups that assisted the opposition leader. “We are still looking for them, and to eliminate the groups who damage the nation and happiness of the people,” he said.

The prime minister was backed up by an Interior Ministry official, speaking on the condition of anonymity, who said the ministry would continue to investigate other opposition lawmakers who were “close to the US”.

The recent targeting of the US comes in the wake of what is widely characterised as Cambodia’s ever-growing bonhomie with Asian powerhouse China.

In a press conference yesterday, Chinese Foreign Ministry spokesperson Geng Shuang responded to questions about Sokha’s arrest by saying China “has always supported Cambodia in following the development path suited to its national conditions and the Cambodian government’s effort to uphold national security and stability”.

However, international condemnation of Sokha’s arrest continued to flow in yesterday, with the EU calling it a breach of his parliamentary immunity and – along with a clampdown on NGOs and independent media – a “further effort to restrict the democratic space in Cambodia”. Statements were also released by the Cambodian Australian Association, the Australian Embassy in Cambodia and the UK’s Minister for Asia Mark Fields, all denouncing the arrest.

Zeid Ra’ad Al Hussein, UN High Commissioner for Human Rights, said he was “seriously concerned” at Sokha’s arrest, and criticised statements by Hun Sen and senior government officials for presuming guilt.

Though the US appears to increasingly preoccupy Hun Sen, Carl Thayer, of the University of New South Wales, said Cambodia was no longer on the US’s radar, with the premier clearly casting “his die in favour of China”. And while the local US Embassy has been pushing back, he added, there wasn’t much coming out of the undermanned US State Department.

Following the expulsion of pro-democracy NGO National Democratic Institute last month, the US Embassy in Phnom Penh questioned the government’s commitment to democracy and called out the Foreign Ministry’s tardiness in responding to the group’s NGO application. NDI’s alleged delinquency was used as justification for its ouster.

Thayer contended that if the government persisted with its recent repressive ways there was a possibility of a strong reaction from the US Congress. “Cambodia has a special deal to export garments and textiles to the United States. This is Hun Sen’s Achilles heel. Cambodia can’t sell these exports to China,” he said.

Paul Chambers, lecturer at Naresuan University in Thailand, said the use of anti-US nationalism was with an eye to easing the ruling party’s anxieties over next year’s crucial elections, and demonstrated the government was unconcerned about upsetting the Trump administration.

But even as attacks on the US, and even the European Union, escalate, Chambers said the pivot to China could be a mistake in the long run. “Pivoting completely toward China might be foolhardy unless the Cambodian government wants to descend into complete economic dependency on Beijing,” he said.

Sebastian Strangio, author of Hun Sen’s Cambodia, said with the government’s shedding of any semblance of democracy and the fear-mongering about US interference, the country was heading into “uncharted territory now”. “This has the flavor of a night of long knives, with the CPP settling accounts with a wide variety of ‘enemies’ whose legitimacy and existence it has never accepted.”

Additional Reporting by Meas Sokchea