North Korea has been moving airplanes and boosting defences 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, 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 US President Donald Trump had declared war on North Korea and that Pyongyang reserved the right to take countermeasures, including shooting down US bombers even if they are not in its air space.
Meanwhile, South Korea urged the United States to help dial down tensions with the North, after Pyongyang accused President Donald Trump of declaring war. ''It is very likely that North Korea will conduct further provocations,'' South Korean foreign minister Kang Kyung-wha said in a speech in Washington on Monday.
''It is imperative that we, Korea and the US together, manage the situation … in order to prevent further escalation of tensions or any kind of accidental military clashes which can quickly go out of control.''