With tensions rising on the Korean peninsula, China is calling for calm and urging all parties to avoid "provocative actions."
President Donald Trump hit the phones Sunday to speak with Chinese President Xi Jinping and Japan's Prime Minister Shinzo Abe, with North Korea dominating the conversation. Trump has long called on China to rein in its unruly neighbor.
According to Chinese state media, Xi told Trump China is strongly against any action that would violate UN Security Council resolutions and added that the Korean Peninsula nuclear issue can only be solved if all parties take responsibility and work together.
Abe, after the phone call, told reporters he would "continue to maintain close contact with the US, and maintain an advanced alert monitoring system."
"North Korea's nukes and missiles are an issue for the international community, but it is also a serious security threat to Japan," Abe said.
Xi's comments come on the back of increasing signs that China may be getting fed up with continued nuclear bluster from long-time ally North Korea and tilting toward the United States.
The weekend saw mercury rise on the Korean peninsula when North Korea threatened to sink a US aircraft carrier conducting drills in the region.
State-run newspaper Rodong Sinmun said the country is ready to illustrate its "military force" by sinking a "nuclear-powered aircraft carrier with a single strike."
The newspaper claimed Pyongyang has weaponry that "can reach continental US and Asia Pacific region" and the "absolute weapon," a hydrogen bomb. CNN cannot independently verify those claims. The editorial is not unusual for North Korean state media, which often responds to perceived threats from the US and its allies with inflammatory language.
Hours later, Pentagon spokesman Gary Ross said the US would call on North Korea "to refrain from provocative, destabilizing actions and rhetoric, and to make the strategic choice to fulfill its international obligations and commitments and return to serious talks."
"North Korea's unlawful weapons programs represent a clear, grave threat to US national security," Ross added.
The aircraft carrier, USS Carl Vinson, is part of a navy strike group currently conducting drills with two Japanese destroyers in the western Pacific Ocean. South Korea is in ongoing discussions with the US Navy about holding its own joint drills with the Vinson strike group, South Korean Defense Ministry Spokesman Moon Sang-gyun said Monday.
US citizen detained
North Korea also detained a US citizen as he tried to leave the capital Pyongyang.
Kim Sang Duk, also known as Tony Kim, was detained as he was about to fly out of Pyongyang International Airport on Saturday morning.
He was teaching at Pyongyang University of Science and Technology (PUST), a statement from the school said.
The university said the detention "is related to an investigation into matters not connected in any way with the work of PUST."
The detention was also confirmed by Martina Aberg, deputy chief of mission at the Swedish Embassy in Pyongyang.
Gary Locke, a former US ambassador to China, told CNN the detention is North Korea trying to get as many "bargaining chips" as possible to make it more difficult for the United States.
"This is only going to inflame the situation and make it more difficult for us to resolve the overarching issue of getting North Korea to stop developing a nuclear weapon," Locke said.
However, Michael Madden, a visiting scholar at the US Korea Institute, cautioned against reading too much into the detention, saying the North Koreans may announce charges after the Tuesday celebrations are over.
"There may be politics at play but all of the people detained by North Korea have been in violation of North Korean law," he said. ""If they (the North Koreans) have something, they'll let us know."
At least two other US citizens are currently in North Korean custody.
Added to the high-tension weekend are fears that North Korea may conduct a nuclear test Tuesday, when the country celebrates the 85th anniversary of the founding of the Korean People's Army. Analysts said earlier this month that North Korea's only nuclear site is "primed and ready" for another test.
The Pentagon Sunday called on the communist nation to avoid destabilizing the situation further.
Madden believes a nuclear test is unlikely and told CNN North Korea would probably conduct a combined forces exercise instead.
"Kim Jong Un will probably watch some military exercises involving all three of North Korea's conventional military branches," Madden told CNN.
In lieu of that, Pyongyang may test another missile.
"We probably would've seen a nuclear detonation at this point," he said. "They don't generally do nuclear weapons on holidays themselves. They tend to do them a few days before holidays."
But South Korea's Unification Ministry said Friday it will be on high alert in case North Korea conducts a test on the holiday.
Pyongyang often uses holidays to carry out actions the US and its allies see as provocative.
It conducted a failed missile test a day after the Day of the Sun, the country's most important holiday, earlier this month, but not a nuclear test, which some predicted would happen.