N Korea threatens military action

As US and South Korean warships circled the waters near the disputed maritime border, the UN Security Council continued its attempts to hammer out a new resolution against Kim Jong-il's regime.

It follows a nuclear test blast by North Korea on Monday, a move that was quickly followed by a number of missile launches and the reported resumption of the country's nuclear programme.

The war of words between North Korea and its southern neighbour escalated on Wednesday.

After Seoul announced that it is to join the US-led Proliferation Security Initiative - a programme to intercept and search ships suspected of aiding nuclear proliferation - the North hit back with belligerent warnings of possible retaliation.

In a statement, Pyongyang's Committee for the Peaceful Reunification of Korea said: "Now that the South Korean puppets were so ridiculous as to join in the said racket and dare declare a war against compatriots (North Korea is) compelled to take a decisive measure."

The regime warned that any attempt to stop and board its ships would be seen as a "grave violation", adding that the US and South Korea should "bear in mind that the (North) has tremendous military muscle and its own method of strike to conquer any targets in its vicinity at one stroke or hit the US on the raw, if necessary."

The comments come amid reports that US spy satellites have detected signs that North Korea had restarted its main Yongbyon nuclear plant.

Downing Street expressed "concern" about the latest developments.

Prime Minister Gordon Brown's spokesman said: "This is clearly a further unnecessary and provocative act by North Korea which will do nothing to advance the prospects for regional security and will only serve to isolate the regime further."