South Korea says it would 'annihilate' Pyongyang if North starts nuclear war

Military sources says the country has a secret plan to reduce the city to ashes

South Korea has a secret plan to "annihilate" Pyongyang if the North Korean regime shows any sign of mounting a nuclear attack, the country's largest news agency has reported.

An unnamed military source told Yonhap that every part of the North Korean capital will be "completely destroyed by ballistic missiles and high-explosive shells".

Those districts which are thought to be hiding the leadership would be particularly targeted and the city "will be reduced to ashes and removed from the map".

Yonhap has close ties to the South Korean government and is publicly funded.

It came just days after North Korea launched what it said was its fifth nuclear test on Friday.

The international community is said to be considering its response with the US saying it is considering imposing sanctions alongside those imposed by the UN Security Council, Japan and South Korea.

The US special envoy for North Korea, Sung Kim, said: "In addition to action in the Security Council, both the US and Japan, together with the Republic of Korea, will be looking at unilateral measures, as well as bilateral measures, as well as possible trilateral cooperation.

"We will be working very closely in the Security Council and beyond to come up with the strongest possible measure against North Korea's latest actions".

But Pyongyang responded to the US warning by saying the threat of "meaningless sanctions" was "laughable".

On Saturday, South Korean's foreign minister, Yun Byung-se, said the North's nuclear capability appeared to be developing fast.

Mr Yun said the latest tests showed North Korean leader Kim Jong-un was unlikely to change course and tougher sanctions were needed to apply "unbearable pain on the North to leave no choice but to change".

Under the 32-year-old, who took over control of the isolated state after the death of his father Kim Jong Il in 2011, North Korea has sped up its nuclear weapons programme despite the UN's economics sanctions against it being tightened in March.

South Korea's President Park Geun-hye said Kim was "mentally out of control", blind to all the warnings of foreign powers and "the patience of the international community has come to the limit".

Under Kim's leadership it is believed there has been a wide ranging purge of senior officials who have been executed for falling out with him.

He denounced his own uncle Jang Song-thaek as "despicable human scum" when he announced his execution in December 2013.

Additional reporting by agencies