US Secretary of State Mike Pompeo (3rd L) shakes hands with North Korea's Foreign Minister Ri Yong Ho (3rd R) as they arrive for a group photo at the ASEAN Regional Forum Retreat during the 51st Association of Southeast Asian Nations (ASEAN) Ministerial Meeting (AMM) in Singapore on August 4, 2018. - Leaders, ministers and representatives are meeting in the city-state from August 1 to 4 for the ASEAN Ministerial Meeting (AMM). (Photo by Mohd RASFAN / AFP)        (Photo credit should read MOHD RASFAN/AFP/Getty Images)
MOHD RASFAN/AFP/AFP/Getty Images
US Secretary of State Mike Pompeo (3rd L) shakes hands with North Korea's Foreign Minister Ri Yong Ho (3rd R) as they arrive for a group photo at the ASEAN Regional Forum Retreat during the 51st Association of Southeast Asian Nations (ASEAN) Ministerial Meeting (AMM) in Singapore on August 4, 2018. - Leaders, ministers and representatives are meeting in the city-state from August 1 to 4 for the ASEAN Ministerial Meeting (AMM). (Photo by Mohd RASFAN / AFP) (Photo credit should read MOHD RASFAN/AFP/Getty Images)
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A letter from US President Donald Trump to North Korean leader Kim Jong Un was given Saturday to North Korea’s foreign minister at the Association of Southeast Asian Nations (ASEAN) meeting, US Secretary of State Mike Pompeo tweeted.

Trump’s letter comes in response to a letter he received this week from Kim, according to State Department spokeswoman Heather Nauert. The letter from the President was delivered to North Korean Foreign Minister Ri Yong Ho after Pompeo shook hands and spoke with Ri at the ASEAN meeting in Singapore, Nauert said.

US Ambassador to the Philippines Sung Kim handed the Trump letter to Ri, and Ri thanked him, Nauert said. Sung Kim was previously an ambassador to South Korea and a special representative for North Korea policy.

While attending the ASEAN meeting Saturday, Pompeo and Ri approached each other and Pompeo told Ri they should talk again soon, according to an account from Nauert. She said Ri replied, “There are many productive conversations to be had.”

Asked what the handshake between the two diplomats might represent, Nauert said, “Anytime you have conversations or interactions like that, especially given where our two countries were one year ago, is a step in the right direction.”

Trump revealed Thursday he had received a letter from Kim Jong Un when the US President tweeted his thanks to Kim after the possible remains of American war dead from the Korean War arrived back on US soil. The White House confirmed that Trump had received the letter Wednesday from North Korea’s leader.

New flare-up over sanctions

Despite the friendly exchange between Pompeo and Ri, there were signs of ongoing tensions between the United States and North Korea over economic sanctions to spur the country to denuclearize.

Ri said Saturday that denuclearization by North Korea should happen “phase by phase,” and a Ri statement posted in the media room at the ASEAN forum criticized the US for “raising its voice louder for maintaining the sanctions against the DPRK.”

The US announced new sanctions Friday against a Russian bank for helping the North Korean regime facilitate illicit financial activity and, as a result, develop its nuclear weapons program.

“We expect the Russians and all countries to abide by the UN Security Council resolutions and enforce sanctions on North Korea,” Pompeo told journalists in Singapore. “Any violation that detracts from the world’s goal of finally fully denuclearizing North Korea would be something that America would take very seriously.”

CNN’s Jennifer Hauser in Atlanta and Aaron Pellish in Washington contributed to this story.