The United States on Tuesday dismissed the claimed ability to strike US mainland with missiles by the Democratic People's Republic of Korea (DPRK), saying the threat will achieve nothing.

"Well, certainly, rather than bragging about its missile capability they ought to be feeding their own people, would be our first comment," said State Department spokeswoman Victoria Nuland.

"The DPRK needs to understand that it will achieve nothing by threats or provocations. That's only gonna undermine their efforts to get back into conversation with the international community," she told reporters at a regular press briefing.

A spokesman for the DPRK's National Defense Commission announced earlier in the day that the country is equipped with strategic rocket forces now able to place the US mainland territory, South Korea, Japan and Guam within its target range.

"We are well prepared to fight with nuclear (weapons) against any nuclear (attacks) by the US and its followers," the spokesman said, vowing to launch all-out efforts to match the United States and South Korea.

The announcement came after the Republic of Korea (ROK) unveiled on Sunday a revised pact with the United States, which allows Seoul to develop ballistic missiles with a tripled range of 800 kilometers to cover the entire Korean Peninsula, as part of its efforts to better respond to perceived missile threats from the North.

Pyongyang's arsenal includes intermediate-range ballistic missiles with a range of 3,000 kilometers capable of striking the entire Korean Peninsula as well as US military installations in Japan and Guam.

"I'd just underscore that under UN Security Council Resolutions 1718 and 1874, North Korea is required to suspend all activities related to the ballistic missile program," Nuland said.

She claimed that changes made by Washington and Seoul in the missile guidance are "defensive in nature," adding "I would note that we haven't changed these ranges or capabilities since 2001 at a time when the North has been very clearly working and boasting about their own capabilities."

Nuland declined to comment on DPRK's striking capability, saying "I'm not going to get into intelligence here. You can imagine. But they know what they need to do if they want to get back into a conversation with us."

Washington is planning a major expansion of missile defenses in Asia to cope primarily with threats from the DPRK, The Wall Street Journal reported in August.