Two US B-1 bombers flew over the Korean peninsula Tuesday in a planned bilateral training mission with Japanese and South Korean F-15 fighter jets, a US military official told CNN. The US regularly conducts “assurance and deterrence” bomber flights with its military partners in the region, but the drills are often criticized by North Korea as provocative acts. “These flights with Japan and the Republic of Korea (ROK) demonstrate solidarity between Japan, ROK and the US to defend against provocative and destabilizing actions in the Pacific theater,” a US military official told CNN. “We can launch and operate long-range bombers over the Korean peninsula on very short notice, and we hope not to have to do that,” Pentagon spokesman US Navy Capt. Jeff Davis said. The 10-hour mission was carried out by two US Air Force B-1B Lancers assigned to the 9th Expeditionary Bomb Squadron from Dyess Air Force Base, Texas, a US military official told CNN. The bombers flew from Andersen Air Force Base, Guam, in the vicinity of Kyushu, Japan, the East China Sea, and the Korean peninsula. They were joined by Japanese and Korean F-15s performing two separate bilateral missions, the official said. US bombers have maintained a presence in the Pacific since 2004. US military flexing Tuesday’s bomber flight is just the latest demonstration of US military might in recent months aimed at sending a message to North Korea and its leader Kim Jong Un – and the sixth B-1 bomber flight conducted by the US since April 1. Despite a consistent US military presence in his backyard, Kim has defiantly continued to march toward developing a long-range nuclear missile. Earlier this year, Beijing called on Pyongyang to suspend its nuclear and missile testing while calling on the US to stop military exercises on and near the Korean Peninsula, which North Korea sees as a threat to its sovereignty. But neither the US nor North Korea has showed signs of compromising. North Korea continues to test missiles at an unprecedented rate, while US warships and aircraft have maintained a consistent presence in the region for months. Trump’s confusing North Korea tweet While the US conducts bomber flights in the region on a routine basis, Tuesday’s joint training mission is particularly noteworthy as it comes just one day after the death of Otto Warmbier – a 22-year-old American who was detained in North Korea for 17 months. The North Korean government handed Warmbier over to US authorities in a vegetative state last week and his death has spurred calls for a US response from several lawmakers. Trump called Warmbier’s death at the hands of North Korea a “disgrace,” and took to Twitter on Tuesday to offer additional thoughts about China’s role in reining in Pyongyang: “While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!” Multiple US officials told CNN they are checking on what the President meant by “not worked out.” One Trump administration official said bluntly they didn’t know what the President was referencing when asked what the tweet meant. Another said there was no meeting earlier in the day that they feel could have spurred this comment or that that tweet foretold some sort of action against North Korea. White House press secretary Sean Spicer on Tuesday offered few details about how the US plans to respond to Warmbier’s death, promising only that the US will “continue to apply economic and political pressure” to change North Korea’s behavior. “The President has spoken very clearly about how he and the first lady and our country feels about the loss of this American,” Spicer said. Spicer said the US is continuing to work with China to apply pressure on North Korea and said the US has seen “positive movement” with China. The US will “continue to work with them and others to put the appropriate pressure on North Korea to change the behavior of this regime,” Spicer said. Asked whether Trump would still consider meeting with Kim Jong Un given the right conditions, Spicer said: “Clearly we’re moving further away, not closer, to those conditions being met.” No sitting US president has ever met with the leader of North Korea while in power.