The two leaders will meet at the end of the month at the Group of 20 gathering in Buenos Aires.

Mr. Pence’s remarks came after the release of a congressional report that said China appeared to have eased up on the enforcement of sanctions against North Korea. The annual report by the U.S.-China Economic and Security Review Commission asked the United States Treasury Department to list Chinese businesses, entities and individuals doing business with North Korea that might be subject to United States sanctions.

Also on Thursday, a spokesman for the Chinese Ministry of Commerce confirmed that trade talks with the United States had resumed following a phone call this month between Mr. Trump and Mr. Xi. Those talks had been on hiatus since August, with Mr. Trump’s top economic advisers feuding over how the United States should proceed.

Mr. Pence also said that he had a cordial encounter with President Vladimir V. Putin of Russia on Tuesday at the gala dinner hosted by the regional bloc, known as Asean.

“We exchanged greetings, but nothing more than that,” he said of Mr. Putin, whose July meeting with Mr. Trump drew fierce criticism in the United States over what many viewed as Mr. Trump’s fawning behavior. Mr. Pence and Mr. Putin also had a brief conversation on Thursday.

Mr. Pence is essentially standing in for Mr. Trump at the Asean meeting, and the president’s absence was conspicuous; not only is Mr. Putin in Singapore, but Mr. Xi will attend the annual Asia-Pacific Economic Cooperation leaders forum this weekend in Papua New Guinea.