Impoverished North Korea should stop bragging about its missile capability and instead ensure it feeds its own people, a top US official said Tuesday.

Reacting to Pyongyang's claims that it possessed rockets capable of striking the US mainland, State Department spokeswoman Victoria Nuland said North Korea should realize threats and provocation will achieve nothing.

"That's only going to undermine their efforts to get back in the conversation with the international community," Nuland said.

"Rather than bragging about its missile capability, they ought to be feeding their own people," she told journalists.

While Nuland refused to discuss whether the United States was taking Pyongyang's claims seriously, analysts have largely dismissed them as bluster.

In a statement carried by the official Korean Central News Agency (KCNA), a spokesman for the North's National Defense Commission said the military had "strategic rocket forces" with a "scope of strike" that not only covered US and South Korean bases in South Korea, "but also Japan, Guam and the US mainland."

The comments came after South Korea announced on Sunday a deal with the United States to almost triple the range of its missiles to 800 kilometers (500 miles) to cover the whole of North Korea.

Nuland highlighted that the changes in the missile guidance with Seoul were "defensive in nature," adding that under UN Security Council resolutions "North Korea is required to suspend all activities related to the ballistic missile program."

"They know what they need to do if they want to get back into a conversation with us. And again, this is boasting about something rather than taking care of the needs of their own people," she said.

The UN World Food Program said in late 2011 that one-third of North Korean children under five are chronically malnourished.

And UN agencies, after a visit to the North, estimated last November that three million people would need food aid in 2012.