SEOUL (BLOOMBERG) - North Korea warned that a nuclear war "may break out any moment" as the United States and South Korea began one of the largest joint naval drills off both the east and west coasts of the peninsula.

Mr Kim In Ryong, North Korea's deputy ambassador to the United Nations, said on Monday (Oct 16) that his nation had become a "full-fledged nuclear power which possesses the delivery means of various ranges" and warned that "the entire US mainland is within our firing range".

He also called North Korea "a responsible nuclear state".

"As long as one does not take part in the US military actions against the DPRK, we have no intention to use or threaten to use nuclear weapons against any other country," Mr Kim said, referring to his country's formal name.

The comments are similar to other warnings that North Korea has made over the past few months as tensions have increased with US President Donald Trump's administration. The regime of North Korea leader Kim Jong Un has repeatedly said it needs the capability to strike the US with a nuclear weapon in order to deter an American attack.

South Korean military officials are preparing for another possible missile launch from North Korea this week to counter the US-South Korea drills, which include an American aircraft carrier and a nuclear submarine. China's Communist Party will also start its most important political meeting in five years on Wednesday.

Russia on Monday urged the US to reduce military drills near North Korea, reiterating a proposal for both sides to step back and calm tensions.

"I don't remember a situation when the feeling of a coming disaster is so clear," Tass news agency cited Russian Ambassador to North Korea Alexander Matsegora as saying.

Russia's Interfax newswire reported on Monday that a meeting is possible this week between Mr Joseph Yun, the US representative for North Korea, and Ms Choe Son Hui, head of the North American department at North Korea's foreign ministry. Both are attending a non-proliferation conference in Moscow this week, it said.