North Korea has threatened to sink Japan and said the US should be “beaten to death like a rabid dog” after the two countries spearheaded fresh UN Security Council sanctions in response to the regimes nuclear test earlier this month, a media report said.

The Korea Asia-Pacific peace committee, which oversees North Korea’s relations with the outside world, described the UN Security Council, which passed a new round of sanctions earlier this week, as a “tool of evil” in the pay of Washington, and called for it to be broken up, the Guardian newspaper reported on Thursday.

“The four islands of the (Japanese) archipelago should be sunken into the sea by the nuclear bomb of Juche,” the committee said in a statement carried by the official KCNA news agency.

It is the first time that Pyongyang has issued an explicit threat to Japan since it fired a medium-range ballistic missile over the northern Japanese island of Hokkaido in August end.

“Japan is no longer needed to exist near us,” the committee said.

The 15-member Security Council voted unanimously in support of a US-drafted resolution condemning the missile test conducted by North Korea on September 3 and imposed measures that include a ban on its textile imports and restrictions on oil exports to the country.

In response, the committee said the US should be “beaten to death like a rabid dog” for the “heinous sanctions resolution”.

“Let’s reduce the US mainland into ashes and darkness. Let’s vent our spite with mobilisation of all retaliation means which have been prepared till now,” it said.

Japan’s top government spokesman, Yoshihide Suga, described the statement as “extremely provocative and egregious”.

A new report has claimed that the detonation of what North Korea claimed was a hydrogen bomb involved a device with an estimated yield of 250 kilotons — making it far more powerful than initially thought, the report said.

Japan’s public broadcaster NHK claimed on Thursday that US and North Korean officials had met “secretly” on the sidelines of a security forum in Switzerland earlier this month.

The report did not offer details, but said that Choe Kang-il, deputy Director General for North American affairs at the North Korean Foreign Ministry, and Evans Revere, a former senior official at the State Department, had raised North Korea’s ballistic missile and nuclear tests.

While Japan’s Prime Minister Shinzo Abe has refused to consider negotiations unless Pyongyang abandons its nuclear weapons programme, an MP had claimed that support was rising inside the governing Liberal Democratic party for possible engagement with the regime, said the report.