Story highlights North Korea's top diplomat accused Trump of declaring war on Monday

Officials: US bombers flew close to North Korean mainland on Saturday

Washington (CNN) US President Donald Trump issued a familiar warning to North Korea on Tuesday, saying the US is prepared to use "devastating" military action if necessary -- as two defense officials tell CNN that the rogue nation has moved a small number of fighter jets, external fuel tanks and air-to-air missiles to a base on its eastern coast to boost military readiness.

The officials would not go beyond saying a small number of assets had been moved by the regime to a known airfield in the eastern part of the country.

The move was seen in US satellite imagery and is viewed by the US as a North Korean effort to boost its military readiness in the eastern sector. It would give the aircraft an ability to fly eastward further than its estimated 900-mile range.

Imagery so far has observed Mig-29 aircraft at the site. Some missiles and fuel tanks are on the planes, but for now, no single jet is carrying both the external fuel tanks and the missiles.

On Monday, the North Korean Foreign Minister Ri Yong Ho claimed US President Donald Trump had "declared a war" on his country, and threatened to shoot down US aircraft flying off its coastline even if they were in international airspace.

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