South Korea's defence ministry said Friday it would expand its cyber warfare unit to help combat growing Internet attacks from North Korea.

The ministry said its cyber command, launched in January last year, would increase the number of personnel from 400 to 500, following an earlier announcement that it would open a cyber warfare school next year.

North Korea reportedly maintains elite hacker units.

Seoul accused Pyongyang of staging cyber attacks on websites of major South Korean government agencies and financial institutions in March this year and in July 2009.

Pyongyang rejected those allegations, accusing Seoul of inventing the charges to raise tensions.

In May South Korea said a North Korean cyber attack paralysed operations at one of its largest banks.