The United States Friday called on North Korea not to take any further provocative steps, as a US think tank said Pyongyang was preparing a launchpad that could pave the way to firing a long-range missile.

Asked about media reports that North Korea, also known as the DPRK, has told China it is preparing further nuclear tests, State Department spokeswoman Victoria Nuland said such moves would just "lead to more isolation."

"The United States calls on the DPRK to refrain from additional provocative actions that would violate its international obligations and run counter to its commitments," she told journalists.

UN Security Council resolutions insist North Korea should not carry out any further nuclear tests, or face further global sanctions.

There was global outrage after Pyongyang on Tuesday defiantly carried out its third nuclear test, saying it was responding to US "hostility" after the UN Security Council condemned its last missile launch two months ago.

"The DPRK is not going to achieve anything in terms of the health, wealth, safety, (or) future of its own people by these kinds of continued provocative actions," Nuland said.

White House spokesman Josh Earnest, speaking aboard Air Force One, also stressed that Pyongyang should abide by UN resolutions.

"We encourage the North Koreans to live up to their international obligations, abandon their nuclear program and work with the rest of the international community to become a responsible member of the international community," he said.

38 North, a blog of the US-Korea Institute at Johns Hopkins University, said Thursday it had analyzed satellite photos that it said showed possible assistance from Iran at the Tonghae Satellite Launching Ground in northeastern North Korea.

38 North said a commercial satellite photograph taken on January 5 showed "important progress" since the area was hit with typhoons last year and indicated activity that was consistent with preparations for a launch.

But the website said there was not enough evidence to support speculation that North Korea could raise the stakes by testing its KN-08, a new missile with potential intercontinental range first displayed in a parade in April.

The website said that North Korea likely was preparing to test much larger rockets by the time the site is completed in 2016.

US mulls calls to restore N. Korea to terror list
Washington (AFP) Feb 15, 2013 - The United States has not decided whether to put North Korea back on a blacklist of state sponsors of terrorism, but its status is regularly reviewed, a top US official said Friday.

The comments came as the US House of Representatives Friday overwhelmingly passed a resolution condemning North Korea's nuclear test earlier this week, and urging the administration to apply all available sanctions to Pyongyang.

North Korea will also likely be raised in talks next week in Washington between Japanese Prime Minister Shinzo Abe and US President Barack Obama.

The White House said in a statement Friday that Obama was looking "forward to in-depth discussions" with Abe on a range of bilateral and global issues as well as "the US-Japan security alliance, economic and trade issues."

North Korea was added to the State Department's blacklist of state sponsors of terrorism on January 20, 1988, following the bombing by its agents of a KAL plane on November 29, 1987 which killed all 115 on board.

But it was removed in October 2008 under then president George W. Bush, when the State Department said the North was not known to have sponsored any terrorist acts since that bombing.

State Department spokeswoman Victoria Nuland told journalists Friday there was nothing new to reveal, but stressed the US constantly reviews intelligence "to determine whether the facts would put them back in that category."

"Countries that have a track record of past terrorist activity, that have been removed from the list, are regularly reviewed to check whether that kind of behavior has resumed," she added.

Under US law a country can only be designated as a state sponsor of terrorism if the secretary of state determines that the government "has repeatedly provided support for acts of international terrorism," she said.

Republican Representative Ileana Ros-Lehtinen put the bipartisan draft bill before the House which implicitly calls for Pyongyang to be redesignated a state sponsor of terrorism -- an exclusive club which includes Cuba, Iran, Sudan and Syria.

North Korean leader Kim Jong-un "has made his priorities clear: to obtain a nuclear weapon and to proliferate nuclear technology with rogue regimes, such as Iran and Syria," Ros-Lehtinen said in a statement.

"I call upon the administration to take the appropriate action necessary to designate North Korea as a state sponsor of terrorism and stand in solidarity with our South Korean and Japanese allies," Ros-Lehtinen said.