SEOUL (Reuters) - North Korean state media on Monday urged the United States to drop sanctions, as South Korea said it was investigating nine cases of coal shipments that potentially violated U.N. resolutions.

FILE PHOTO - U.S. President Donald Trump and North Korea's leader Kim Jong Un shake hands during the signing of a document after their summit at the Capella Hotel on Sentosa island in Singapore June 12, 2018. Susan Walsh/Pool via Reuters/File Photo

Pyongyang had demonstrated good faith by ending nuclear weapons testing and returning the remains of U.S. troops killed in the 1950-53 Korean War, and the resolutions had lost a reason to exist, said the Rodong Sinmun, a mouthpiece of the ruling Workers’ Party.

The statements came days after a confidential United Nations report concluded that North Korea had not halted nuclear and missile program, in breach of U.N. resolutions, and continued illegal trade in oil, coal and other commodities.

South Korea is examining nine cases in which coal from North Korea disguised as Russian products was possibly brought in, Seoul’s foreign ministry and customs officials said.

They declined to detail the number of ships or identify the companies involved, saying the investigation was in the final phase following raids and forensic analysis, but some cases might prove lawful.

North Korea and the United States vowed to work to end Pyongyang’s weapons program at a landmark summit in June in Singapore, but have struggled to reach a pact to meet that goal.

The Rodong Sinmun accused Washington of “acting opposite” to its plan to improve ties, despite goodwill gestures by Pyongyang, such as a moratorium on nuclear and missile tests, the dismantling of a nuclear site, and the return of the remains of U.S. soldiers killed in the Korean War.

“There have been outrageous arguments coming out of the U.S. State Department that it won’t ease sanctions until a denuclearisation is completed, and reinforcing sanctions is a way to raise its negotiating power,” it said in an editorial.

“How could the sanctions, which were a stick the U.S. administration had brandished as part of its hostile policy against us, promote the two countries’ amity?”

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The editorial, which accompanied front-page articles and photographs of leader Kim Jong Un’s visit to a catfish farm, was a fresh sign of Pyongyang’s frustration over the slow-moving nuclear talks.

Under President Donald Trump, the United States pushed the United Nations to impose tough sanctions on North Korea as Kim conducted a string of missile and nuclear tests last year.

At a security forum on Saturday, the two sides sparred over the Singapore pact, with U.S. Secretary of State Mike Pompeo calling for sanctions against Pyongyang to be maintained, and his North Korean counterpart, Ri Yong Ho, criticizing Washington for “retreating” from ending the war.

Pompeo suggested the North’s continued work on its weapons program was inconsistent with Kim’s commitment to denuclearize, but expressed optimism it would be achieved.

Returning to Washington, Pompeo played down the exchange with Ri, saying the tone was far different from last year.

“The minister made very clear of their continued commitment to denuclearize,” Pompeo told reporters traveling with him.

“I probably don’t have his words exactly right, but it’s pretty close. Compare the anger, frankly, over years and years, and hatred, as spewed by the North Koreans; his comments were different.”

North Korea’s propaganda websites on Monday also urged the United States to drop sanctions and build trust.

One of them, Uriminzokkiri, lambasted the sanctions and pressure campaign as “anachronistic” and a hurdle to better relations, urging efforts to officially declare an end to the Korean War.

The Korean War ended in an armistice, not a peace treaty, leaving the U.S.-led United Nations forces, including South Korea, technically still at war with the North.

The State Department has said it is committed to building a peace mechanism to replace the armistice, but only after the North abandons its nuclear program.

Maeri, another North Korean website, stressed the need for U.S. action to build confidence in response to the North’s moves to end weapons program and send back the remains.

“It takes two to tango,” it said.

Kim Eui-kyeom, a spokesman for South Korea’s presidential Blue House, said on Monday the government was asking the North to hasten denuclearisation and the United States to show sincerity over the North’s demands for reciprocal steps.