The US is deploying nuclear capable B-52 and B-2 stealth bombers, as well as F-22 stealth fighter jets over South Korea, in what it says is a 'deterrence' in the event of any aggression from the North.

The South Korean President has promised a strong military response to any provocation from Pyongyang, following their threats that the two countries are in a state of war.

President Park Geun-Hye says she's taking the North's threats 'very seriously', and is vowing strong and immediate retaliation.

It comes as North Korea is set to hold its annual parliamentary session, and a day after ruling party leaders vowed to enshrine Pyongyang's right to nuclear weapons in law.