An unnamed military spokesman from North Korea was quoted by China's official news agency Xinhua as saying it viewed the presence of B-52 bombers and nuclear-powered submarines based at a U.S. air force base in Guam as a threat.
"Now that the United States started open nuclear blackmail and threat, North Korea, too, will move to take corresponding military actions," the spokesman said.
South Korean news agency Yonhap reports that North Korea sounded air raid sirens for about an hour Thursday in a civil defense drill. The South Korean military said the sirens may have been a response to the presence of B-52s over South Korean airspace. The bombers were included in last week's joint military drills with South Korea.
The military said the North Korean air raid siren was likely a way to show it's engaged with foreign adversaries, Yonhap reports.
North Korea said recently it would use nuclear weapons in self-defense as a response to growing tensions on the Korean Peninsula.
Pressure on North Korea has mounted in response to the government's Feb. 12 decision to test a nuclear device underground. The government withdrew unilaterally from the armistice that halted the Korean War in the 1950s in response.