The United States called on North Korea to release detained Americans, suggesting that such a move could improve ties between the two nations, weeks after Pyongyang detained an 85-year-old Korean War veteran from the Northern California city of Palo Alto.

Bilateral ties between Washington and Pyongyang had turned particularly hostile earlier this year after Kim Jong-un’s government threatened to launch a nuclear attack on the U.S. and South Korea. Merrill Newman’s detention on Oct. 26 comes a year after North Korea held Korean-American Kenneth Bae, who has been sentenced to 15 years of hard labor.

“North Korea could send a very different signal about its interest in having a different sort of relationship with the United States were it to take that step of releasing our citizens, and it's a matter of some wonderment to me that they haven't yet moved on that,” Glyn Davies, U.S. special representative for North Korea policy, told reporters in Beijing, according to a Reuters report.

Meanwhile, Secretary of State John Kerry termed the latest detention as one of many “disturbing choices by the North Koreans,” during an appearance on MSNBC television.

Newman’s son Jeff Newman told CNN that his father was keen to visit North Korea and to learn about its culture for years. “He arranged this with a travel agent that was recommended and said was approved by the North Korean government for travel of foreigners. He had all the proper visas,” Jeff Newman said.

Davies met with China’s Foreign Minister Wang Yi and China’s special representative for Korean Peninsula affairs, Wu Dawei, on Thursday to discuss a range of issues related to North Korea. “These discussions are the latest in a series of regular ongoing consultations with all of our five-party partners,” State Department spokeswoman Jen Psaki said, according to the official transcript of a press briefing in Washington, D.C. “Both the United States and China agree on the fundamental importance of a denuclearized North Korea.”

Davies will hold discussions in Seoul with his South Korean counterpart before traveling to Tokyo for consultations with his Japanese counterpart, Psaki said.

No U.S. official has formally confirmed the detention of Newman, saying it would be a breach of privacy laws, but the detainee’s family and his neighborhood have confirmed that he was pulled off an airplane moments before it was set to depart from Pyongyang's Sunan International Airport.

Former New Mexico Gov. Bill Richardson, who has taken part in negotiations with North Korea in the past to secure the release of detained Americans, “is in touch with his North Korean contacts,” spokeswoman Caitlin Kelleher told Reuters.