US President Donald Trump's declaration that he intended to end joint military exercises with South Korea has taken some South Korean and US military officials by surprise.
Defence secretary Jim Mattis was not among them, however, with spokeswoman Dana White saying "there were no surprises".
Current and former US defence officials expressed concern at the possibility that the United States would unilaterally halt military exercises without an explicit concession from North Korea lowering the threat from Pyongyang.
"I'm sort of stunned about how much we gave up and how little we got in return," said one former official, saying the decision "borders on irresponsible" and would erode readiness and diminish the credibility of the US-South Korean alliance.
Trump made the remarks at a news conference after his summit with North Korean leader Kim Jong-un in Singapore, calling war games expensive and "provocative", echoing a North Korean criticism that the United States had long rejected.
Trump also said he wants "at some point" to withdraw the American troops currently in South Korea.
"We have right now 32,000 soldiers in South Korea, and I'd like to be able to bring them back home. But that's not part of the equation right now," Trump said.
About 28,500 troops are stationed in South Korea, a legacy of the Korean War, which ended in 1953 in an armistice that left the two Koreas technically still at war.
If implemented, the end of military exercises could be one of the most concrete and controversial moves to arise from Trump's summit with Kim, who pledged to pursue denuclearisation but offered no details.
South Korea's Presidential Blue House said it needed to "to find out the precise meaning or intentions" of Trump's statement, while adding that it was willing to "explore various measures to help the talks move forward more smoothly."
A spokeswoman for US military forces in Korea said they had not received any direction to cease joint military drills.
Mitchell Reiss, who served from 2003-2005 as the US State Department's director of policy planning, said it was important to make such decisions hand-in-hand with South Korea.
"My first question is whether our allies, the South Koreans, were consulted in advance of suspending these military exercises," Reiss said. "My second question is, what did we receive in return for this concession?"