South Korea is urging North Korea to speed up the process of denuclearizing.

Kim Eui-kyeom, a spokesman for the South's presidential Blue House, told reporters on Sunday that Seoul wants Pyongyang to accelerate the denuclearization process, according to South Korea's Yonhap News Agency.

But he also said the U.S. must stick to the promises it made to the North.

"We are asking North Korea to speed up its denuclearization process," Kim said. "And to the U.S., we are asking that it show sincere efforts about corresponding measures that North Korea is demanding."

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During a summit with North Korean leader Kim Jong Un in June, President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE sought to push the denuclearization of the Korean Peninsula in exchange for U.S.-backed development in the cash-starved North.

Trump touted the talks with Kim as a success. But follow-up discussions have hit some snags.

For example, North Korean officials failed to show up at a planned meeting with U.S. officials last month. And media reports have indicated that the North may be continuing to bolster its weapons programs, despite the dialogue with Washington.

But in a sign of cooperation, North Korea returned last week what it said were the remains of dozens of U.S. soldiers killed in the Korean War, making good on at least part of a deal reached by Trump and Kim in June.

U.S. officials and experts still need to determine if the remains are, in fact, those of American service members.