BEIJING – North Korea accused the U.S. and South Korean intelligences agencies on Friday of plotting to kill the nation’s leader, Kim Jong Un, using “biochemical agents.”

The accusation came amid sharply increased tensions between the United States and North Korea over Pyongyang’s nuclear and missile programs.

On Thursday, the House voted overwhelmingly to tighten sanctions on North Korea by targeting its shipping industry and companies that do business with the reclusive state.

The measure, passed by a vote of 419 to 1, would need to be approved by the Senate before being sent to the White House for President Trump to sign into law.

North Korea’s official Korean Central News Agency (KCNA) said Friday that the U.S. Central Intelligence Agency and South Korea’s National Intelligence Agency had bribed a North Korean citizen to “hurt the supreme leadership” using a biochemical substance. KCNA has made similar accusations in the past, none of which have been verified.

The two intelligence agencies, “hotbed of evils in the world, hatched a vicious plot to hurt the supreme leadership of the DPRK,” the news agency said, using the initials of the country’s official name, the Democratic People’s Republic of Korea. The report cited the Ministry of State Security.

But Cui Zhiying, a professor in the Center for Asia-Pacific Studies at Tongji University in Shanghai, said the accusation was unlikely to be true, and more likely just another episode in a “war of words” between the two sides.

“There is no doubt that the United States and South Korea have been thinking about eradicating Kim Jong Un, but it is hard to put into practice,” he said. He said the claim was more likely a North Korean response to “escalating threats” from the U.S. side.

CIA Director Mike Pompeo was in South Korea this week, conducting “detailed security discussions” with his South Korean counterpart and visiting an island near the border between North and South, the U.S. military command in South Korea said in a statement Tuesday.

The Trump administration has not ruled out a military strike against North Korea’s missile program but says it first wants to tighten sanctions against the regime and is even prepared to negotiate in the right circumstances.

Secretary of State Rex Tillerson has said that the administration is not seeking regime change in North Korea, and he told ABC last month that he was “not aware” of any plans to assassinate Kim.

John Delury, a professor of international relations at Yonsei University in Seoul, said one of the North Korean regime’s main narratives is that the country faces relentless hostility from the outside world, driven by the United States.

“That is their central argument as to why they need to develop a military deterrent,” he said. “Whether there is some truth [to the assassination claim] or whether it is entirely fictional, it fits this narrative.”

On Friday, China responded to the events in the U.S. Congress by saying it supported United Nations Security Council resolutions but opposed the imposition of “unilateral sanctions.”

“The current situation on the peninsula is complex and sensitive, and the parties concerned should exercise restraint, in particular to avoid taking actions that stimulate others and to prevent a further escalation of the situation on the peninsula,” Foreign Ministry spokesman Geng Shuang said at a regular news conference.