North Korea is preparing to launch an advanced intercontinental ballistic missile with an enhanced engine that can make it fly longer, a Russian lawmaker told Kyodo News on Monday.

Anton Morozov, a Russian lower house member who visited Pyongyang for five days through Friday, said in a telephone interview that Kim Yong Nam, the president of the Presidium of the Supreme People's Assembly, told him the type and range of the missile being prepared for launch.

Morozov said that Kim showed him a mathematical formula and explained the missile can reach the U.S. West Coast although it is the same type North Korea has fired in the past.

In a meeting with Morozov, North Korea said it was preparing a fresh missile test in a retaliatory move against the United States after President Donald Trump said at a U.N. General Assembly meeting in September that Washington may have to "totally destroy" North Korea if further provocations force it to defend itself or its allies.

North Korea said it took Trump's remark as a declaration of war, according to Morozov.

On the timing of the missile launch, Morozov was told it would be sometime soon but was not briefed on details. He said it could be on Tuesday, which is the anniversary of the foundation of the Workers' Party of Korea.

Although Pyongyang seemed to be preparing for a war, Morozov said he and his colleagues suggested solving the issue through dialogue.