North Korea has been moving airplanes and boosting defenses on its east coast after the United States dispatched B-1B bombers to the Korean peninsula over the weekend, South Korea's Yonhap News Agency reported on Tuesday, citing the country's spy agency.

The United States seemed to have disclosed the flight route of the bombers intentionally because North Korea seemed to be unaware, the report said.

South Korea's National Intelligence Service was unable to confirm the report immediately.

North Korea's foreign minister said on Monday that U.S. President Donald Trump had declared war on North Korea and that Pyongyang reserved the right to take countermeasures, including shooting down U.S. bombers even if they are not in its air space.