Pyongyang, Dec 28 (IANS): Internet and 3G mobile network of North Korea were paralysed again amid bickering between the United States and the former over an earlier cyber attack on Sony Pictures.

At 7.30 p.m. Pyongyang time Saturday, North Korea's internet and 3G mobile network came to a standstill, and had not returned to normal as of 9.30 p.m. Saturday, reported Xinhua.

Earlier in the day, the Policy Department of the National Defence Commission blamed the United States for enduring instability of the country's internet and denied any cyber attack on Sony Pictures.

The United States groundlessly linked the hacking at the Sony Pictures Entertainment to North Korea, a spokesman for the department said in a statement.

The spokesman urged the United States to conduct a joint investigation with North Korea.

The United States accused North Korea of attacking Sony Pictures in late November to deter it from showing a comedy movie titled "The Interview" which features an assassination attempt on North Korea leader Kim Jong Un.

North Korea's internet has been unstable since last weekend, including a complete outage of about nine hours Tuesday.