North Korea lashed out Friday at a new South Korea-Japan intelligence-sharing accord, accusing Seoul of a gross act of betrayal with the "sworn enemy" of the Korean people.

The deal to share defence intelligence -- largely driven by the growing threat of the North's nuclear and missile programmes -- was reached and provisionally signed in Tokyo on Monday.

It was a controversial move in South Korea, where the legacy of Japan's harsh 1910-45 colonial rule of the Korean peninsula is a deep well of anti-Japanese sentiment and a belief that Tokyo has never properly atoned for the abuses of that era.

Tensions between South Korea and Japan are welcomed and even encouraged by North Korea, which seizes any opportunity to drive a wedge between the two key US military allies in the region.

A spokesman for the Korea Asia-Pacific Peace Committee in Pyongyang called the intelligence agreement a "hideous act of treachery aimed to stifle fellow countrymen in the north in league with the sworn enemy of the nation".

In a statement carried by the North's official KCNA news, the spokesman said it was a "dangerous act" that would further raise already-elevated tensions on the Korean peninsula and open a door to Japanese "re-invasion."

The amplified rhetoric will strike a chord in the South, where the main opposition party called Monday's agreement "unpatriotic and humiliating".