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 know as the DPRK, has told China it is also preparing further nuclear tests, State Department spokeswoman Victoria Nuland 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.
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.