On Monday, two US B-1 bombers departed Andersen Air Force base in Guam and conducted a joint drill with South Korea and Japan's air forces over the Korean Peninsula, according to the US Air Force.
Separately, two B-1 bombers also flew over South Korea in late April, according to a US defense official. Bombers also flew near Australia on April 17 and close to the South China Sea on April 11, the official told CNN.
Both missions near Korea were long-planned and there was a decision to keep a relatively low public profile on the flyovers to avoid increasing the regional temperature, the official told CNN.
But the flights were also meant "as a demonstration of the strength of the bilateral alliances between the United States, Japan and the Republic of Korea and reflect broadening trilateral cooperation to defend against common regional threats," according to Lt. Col. Lori Hodge, an Air Force spokesperson.
Pyongyang has accused the US of intentionally carrying out a "military provocation."
"The B-1Bs from Guam sneakily flew over sky above the East Sea (on Monday) and joined cooperative operations with strategic striking means, including the aircraft carrier and nuclear-powered submarine," according to North Korea's state news network.
"Due to the US military provocations that are becoming more explicit day by day, the situation in the Korean peninsula, which is already sensitive, is being driven to a point close to nuclear war," the state-run broadcaster said.
South Korean Defense Ministry spokesman Moon Sang-gyun said Tuesday that the deployment of US bombers was part of an effort to "respond to North Korea's nuclear missile threat and to deter North Korea's provocations."
The second of the two flights came on the same day President Donald Trump said he would be willing to meet with North Korean leader Kim Jong Un "under the right circumstances" to defuse tensions over Pyongyang's nuclear program.
No sitting US president has ever met with the leader of North Korea while in power, and the idea is extremely controversial.
The US has also directed an aircraft carrier-led strike group to the region and deployed a new anti-ballistic missile system to South Korea.
The US use of Guam-based bombers to make a statement on the Korean Peninsula is not new. After North Korea's fourth nuclear test in January 2016, a Guam-based B-52 made the flight.
US bombers have maintained a presence in the Pacific since 2004.