US Secretary of State Hillary Clinton on Tuesday warned North Korea not to go ahead with a rocket launch as she voiced concern that the communist state may also plan more "provocations."

With North Korea apparently ready to launch a long-range rocket within days, Clinton said that the United States was "working around the clock" with allies South Korea and Japan to "sharpen our deterrent."

Clinton said that North Korea's launch plans -- just weeks after the regime signed a deal with Washington to freeze its nuclear and missile programs -- "raises questions about Pyongyang's seriousness in saying that it desires to improve relations with us and its neighbors."

"This launch will give credence to the view that North Korean leaders see improved relations with the outside world as a threat to the existence of their system," Clinton said in a speech to the US Naval Academy.

"And recent history strongly suggests that additional provocations may follow," she said.

Clinton did not elaborate, but a South Korean official earlier said that North Korea appears to be preparing for a third nuclear test after the planned long-range rocket launch.

Meeting earlier in Washington with Japanese Foreign Minister Koichiro Gemba, Clinton said that the United States was consulting with other nations and "we will be pursuing appropriate action."

"If North Korea wants a peaceful, better future for their people, it should not conduct another launch that would be a direct threat to regional security," she told a joint news conference.

Gemba spoke of US-Japanese cooperation if North Korea goes ahead with the launch of a rocket it says will put a satellite into orbit -- an event that most of the rest of the world sees as a disguised missile test.

"The United States and Japan would cooperate with each other and the international community, including the Security Council, would take an appropriate measure," Gemba said.

Neither Clinton nor Gemba explained what they meant by "appropriate" action.

Both top diplomats reiterated that the launch would violate UN Security Council resolutions 1718 and 1874, which ban ballistic missile activity.

US State Department spokeswoman Victoria Nuland voiced concern that the international news media might be "playing" into North Korean propaganda by covering the rocket launch.

"Our concern obviously would be that the North Koreans would use this for propaganda purposes and that... news organizations that cover it extensively might be playing into that," Nuland said.

"But it's obviously your call how to cover this thing," she told reporters during the daily news briefing.

The usually secretive North organized an unprecedented visit for foreign reporters to Tongchang-ri space center in an effort to show its Unha-3 rocket is not a disguised ballistic missile, as claimed by the US and its allies.

The launch is scheduled between April 12 and 16 to mark the 100th anniversary of the birth of North Korea's founding leader Kim Il-Sung, a significant date as Kim's youthful grandson Kim Jong-Un cements his own power.

N. Korea missile tech a 'concern': US commander
Tokyo (AFP) April 11, 2012 - North Korea's increasingly sophisticated missile technology is a concern to Asia and the United States, the new US Pacific commander said Wednesday ahead of Pyongyang's planned rocket launch.

"We have seen over time the North Koreans pursue increasingly sophisticated ballistic missile defence technologies," Admiral Samuel Locklear, the head of the US Pacific Command based in Hawaii, said in Tokyo during his first visit to Japan in the role.

"And I understand that if they are able to achieve their capabilities over the long run that they are pursuing... it will increase the potential ranges of the missile technology that they have and they could proliferate.

"And this... will be a concern for the alliance, a concern for the region as well as a concern for the United States," he said.

He declined to say how far advanced he believed North Korea's missile technology was, but added "hopefully the North Koreans would make the decision to de-escalate... and they would not continue to pursue the missile technology which has a destabilising effect on the security of the region."

Shortly after Locklear spoke, North Korea announced it was fuelling the rocket it says will propel a satellite into orbit to collect data on forests and natural resources within its territory.

The West says it is a disguised ballistic missile test, in violation of a United Nations ban, and fears that North Korea will follow up with a third nuclear test.

Locklear, who oversees more than 300,000 service members and a fleet of aircraft and warships over an area spanning the west coast of the United States to the western border of India, said he knew little about any atomic test.

"Beyond (what) you have seen in that open press reporting, I have no further information," he said.

Locklear was nominated for the post in December after a year in which US President Barack Obama repeatedly stressed the strategic importance of the Asia-Pacific region and vowed to expand the American military's presence, announcing the deployment of up to 2,500 US Marines in Australia.

The admiral told reporters in Tokyo he was looking to strengthen existing alliances in the region.

"When you look at... the rebalancing, you should look at the totality of what's happening within the Japanese-US alliance... the cooperation, the interoperability. It goes well beyond just the issue of ballistic missile defence" that Tokyo and Washington are jointly developing, he said.

"It goes into information-sharing. It goes into cyber. It goes into all the aspects that make a good alliance better."

A US congressional advisory report released last month said China's cyber warfare capabilities would pose a danger to US military forces in the event of a conflict over Taiwan.

The report by defence contractor Northrop Grumman for the US-China Economic and Security Review Commission said China's People's Liberation Army (PLA) has placed great emphasis on what is known as "information confrontation".

The US "commitment to Japan and the region is unwavering, and we are working to ensure that our alliance is fully capable of meeting all the challenges we might face in the future," Locklear said.