By Christian Shepherd and Linda Sieg
BEIJING/TOKYO (Reuters) - With U.S. President Donald Trump setting the course for normalizing ties with North Korea and even saying war games with South Korea would end, China appeared a winner from Tuesday's summit, as Japan tried putting a brave face on the outcome.
Trump and North Korean leader Kim Jong Un pledged on Tuesday to work toward complete denuclearization of the Korean peninsula, and signed a "comprehensive" document at a landmark summit in Singapore.
In turn, Washington committed to provide security guarantees for North Korea, though the joint statement was light on specifics.
At a post-summit press conference, Trump said Washington would end "very provocative" and costly military exercises with South Korea, a move that would rattle Seoul and Tokyo, which rely on the U.S. military for their own security.
China, North Korea's most important economic and diplomatic supporter despite its anger at Pyongyang's nuclear and missile tests, wasted little time with a reminder that U.N. sanctions could be adjusted if North Korea behaved itself.
"The U.N. Security Council resolutions that have been passed say that if North Korea respects and acts in accordance with the resolutions, then sanction measures can be adjusted, including to pause or remove the relevant sanctions," a Foreign Ministry spokesman, Geng Shuang, said at a daily news briefing.
The Global Times, an influential Chinese state-run newspaper, said in an editorial that the time was right to consider "an appropriate reduction of the sanctions".
Brad Glosserman, visiting professor at Japan's Tama University, said China would be pleased with the outcome.
He said that North Korea would be as well.
"Kim – wants a photo op, gets it, got an invitation to the White House," he said. "He has an open door to the weakening of sanctions, no one is going to be putting on the squeeze. Everything North Korea wanted – I see no downside."
Japanese Prime Minister Shinzo Abe put a positive spin on the summit, welcoming the fact that Trump told a news conference he had raised the issue of Japanese abductees, though there was no mention of that in the document signed by Kim and Trump.
Yoji Koda, a retired admiral who commanded the Japanese naval fleet, and is a fellow at the Fairbank Center for Chinese Studies at Harvard University, said the statement contained nothing new or concrete.
"One of the key points that Trump and his advisers made was that the U.S. will not repeat the mistakes of previous deals," he said. "From reading this document I don't think the U.S. will be successful."
South Korea's presidential office said it needs to seek clarity on Trump's intentions after he said Washington will stop joint military exercises.
South Korea's President Moon Jae-in, who has been front and center in efforts to engage the North and Kim himself, pledged complete cooperation.
"My administration will spare no effort in cooperating with the United States, North Korea and the international community to ensure that the agreement can be implemented in its entirety," Moon said in a statement.
But Koda, the retired Japanese admiral, said ending the exercises would be a "clear mistake" and was "too early".
"Alliances are a key element of U.S. global strategy and exercises are a right of the U.S. to use to protect allied nations," he said. "The U.S. should continue joint exercises, they are a signal to China too."
China, which has long suggested a "dual suspension" whereby North Korea suspends its weapons tests and the United States and South Korea suspend military drills, could effectively claim that as an outcome despite not being a party to the summit.
"This joint declaration is in line with the three principles of 'no chaos, no war, and peaceful settlement' proposed by the Chinese government," said Liang Yabin, an associate professor at Beijing's Central Party School, which trains rising officials.
Resolving tensions on the Korean peninsula has obvious benefits for China, especially in bolstering the development of its rust-belt and landlocked northeast.
Beijing has also long feared that a collapse of its isolated neighbor could push waves of refugees into northeastern China, or that nuclear war on the Korean peninsula could contaminate swathes of the country.
The emotional ties are deep too. The two countries fought side by side in the 1950-53 Korean War - a son of Mao Zedong died in the conflict - and China has long viewed North Korea as a useful buffer between it and U.S. forces in South Korea.
While China was not a direct party to the summit, it was nonetheless a presence: Kim met with President Xi Jinping twice in the run-up, and even borrowed an Air China 747 to get to Singapore so he didn't have to rely on his own Soviet-era plane.
(Additional reporting by Tim Kelly in Tokyo, Hyonhee Shin and Heekyong Yang in Seoul, and Yawen Chen and Stella Qiu in Beijing; Writing by Ben Blanchard; Editing by Tony Munroe and Philip McClellan)