The North Korean military on Thursday said it would be prepared to use "precision" weapons to attack US naval bases in Guam and Japan, if provoked.

Pyongyang issued the threat a day after describing practice flights of B-52s over the Korean Peninsula as an "unpardonable provocation." The bombers, capable of delivering nuclear warheads, have been deployed by the US since the 1950s.

"We cannot tolerate the US carrying out nuclear strike drills, setting us as targets, and advertising them as strong warning messages," a spokesman for the North's supreme army command said in a statement carried by state media.

"The US should not forget that the Anderson Airbase in Guam where the B-52s take off, as well as naval bases at Japan's main island and Okinawa, are all within the range of our precision target assets," the statement warned.

The Pentagon has confirmed that the B-52s from the base in Guam had flown over South Korea.

Radio air raid report

Earlier on Thursday, the North was reported to have issued a public air raid alert via radio. South Korea's Unification Ministry said it had picked up the warning being issued just after midnight.

The North Korean threat is the latest in a recent round of saber-rattling after UN sanctions were tightened last month, following the country's third-ever nuclear test.

In response, North Korea threatened the United States and South Korea with the possibility of a pre-emptive nuclear strike.

Annual joint drills between the US and South Korea, codenamed Foal Eagle, began on March 1 for a period of two months.

rc/jm (AFP, Reuters)