North Korea is armed with "powerful modern weapons" capable of defeating the United States, a top military chief in Pyongyang said Wednesday, a claim that matches the country's regular rhetoric but is questioned by experts.

The comments by Vice Marshal Ri Yong Ho at a meeting marking the 80th anniversary of the army's founding came amid increased speculation abroad about the nation's missile arsenal and nuclear ambitions.

Washington worries about the possibility that North Korea might develop a reliable intercontinental ballistic missile and a nuclear bomb small enough to use as a payload.

But outside experts believe that is still a long way off.

Rocket test failures

North Korea has enough plutonium for about four to eight "simple" bombs, according to estimates by scientist Siegfried Hecker of the Center for International Security and Cooperation, but it doesn't yet appear to have the ability to make bombs small enough to mount on a missile. The country's past long-range rocket tests — in 1998, 2006, 2009 and earlier this month — are believed to have ended in failure.

Ri emphasized the importance of strengthening the military to defend North Korea against threats it sees from the United States and South Korea. He called his nation a nuclear and military power and praised new leader Kim Jong Un, believed to be in his late 20s, as a "military strategist" who has been giving the army guidance for years.

"The Korean People's Army is armed with powerful modern weapons ... that can defeat the (U.S.) imperialists at a single blow," he told party and military officials, using familiar descriptions of the country's rivals.

The Associated Press was among foreign news agencies based in Pyongyang allowed to observe the closed meeting, attended by Kim Jong Un.

Ri, who is chief of the army's General Staff, did not provide further details about North Korea's weapons, but his call to arms comes as the United States, Britain and others warn the North against provocations that would further heighten tensions. The Korean peninsula remains officially at war because the 1950-53 Korean War ended with an armistice, not a peace treaty.

Earlier this month, North Korea launched a long-range rocket in what its officials called a failed attempt to put a satellite into space. The launch was decried internationally as a banned test of long-range missile technology.

UN condemnation

The rocket broke into pieces shortly after liftoff. The UN Security Council later condemned the launch as a violation of resolutions prohibiting North Korea from engaging in nuclear and missile activity, and Washington halted a plan to provide the North with much-needed food aid in exchange for a moratorium on nuclear and missile tests.

On Monday, North Korea responded to U.S. and South Korean criticism with threats to reduce South Korean targets "to ashes"within minutes in a particularly sharp warning that followed days of protest rallies held nationwide.

There also are worries that North Korea may conduct a nuclear test, as it did after rocket launches in 2006 and 2009. South Korean intelligence officials say recent satellite images show the North has been digging a new tunnel in what could be preparation for a third atomic test.

U.S. Defence Secretary Leon Panetta warned North Korea not to engage in any further provocation.

He told reporters in Brazil that he had no knowledge of any specific actions being planned by North Korea but said he would "strongly urge" it to avoid any destabilizing acts