Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) suggested on Sunday that China may have pressured North Korea to take a harder line against U.S. negotiators during a recent visit to the isolated country by Secretary of State Mike Pompeo Michael (Mike) Richard PompeoTreasury sanctions individuals, groups tied to Russian malign influence activities Navalny released from hospital after suspected poisoning Overnight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers MORE.

"I see China’s hands all over this," Graham told "Fox News Sunday," citing an ongoing trade war between the U.S. and China as Beijing's possible motivation. "We’re in a fight with China."

Graham's comments came a day after the North Korean foreign ministry released a lengthy statement condemning U.S. negotiators' "gangster-like" demand for denuclearization.

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The criticism suggests that talks between the U.S. and North Korea to end the country's nuclear program may take longer than President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE has said. After the president left a landmark summit with North Korean leader Kim Jong Un last month, he declared that Pyongyang was "no longer a nuclear threat."

Pompeo insisted that his visit to North Korea was "productive." He fired back at the country's criticism, saying if the U.S. requests for denuclearization "were gangster-like, the world is a gangster" — a reference to the widespread condemnation of the North's nuclear ambitions at the United Nations.

Graham placed blame for the North's colder attitude on Chinese influence, saying that the outbreak of a trade war between Beijing and Washington was to blame for the antagonism.

He also warned China against stepping up the trade conflict, saying that the U.S. has "more bullets than they do when it comes to trade."

"We can hurt them more than they hurt us," Graham said, adding that there is "no doubt" in his mind that China is "pulling the North Koreans back."

“And to our North Korean friends, I can’t say the word 'friend' yet," he added. "You asked Pompeo: ‘Did he sleep well?’ If you knew what I knew about what we could do to the leadership of North Korea, you wouldn’t sleep very well.“

— This report was updated at 10:21 a.m.