A long-range rocket launch by North Korea would heighten tensions in the region and lead world powers to put Pyongyang back in the dock at the UN Security Council, UN Secretary General Ban Ki-moon warns.
In New York, China's envoy urged that everything possible should be done to defuse tension over North Korea's plan to conduct a launch that has drawn international criticism.
North Korea's neighbours and the West say the launch - which could blast off within days - is a disguised ballistic missile test. Regional powers also fear it could be the prelude to another nuclear test, a pattern the hermit state set in 2009.
Ban told a news conference in Geneva that the threatened launch of a so-called "application satellite" atop a ballistic missile would worsen relations with North Korea's neighbours.
"I only hope that DPRK authorities will heed the calls of the international community. It is clearly a violation of Security Council resolution 1874," Ban said, referring to the Democratic People's Republic of Korea.
"It seems to me that, considering what measures they have taken until today, by inviting foreign journalists, showing their launching pad, that they may proceed, unfortunately.
"There were many countries in the region to have exercised their influence over DPRK authorities not to go ahead but there is no indication that they may not launch this one. We are very much concerned about this."
In New York, China's Ambassador to the United Nations Li Baodong told reporters: "We have got to do everything possible to defuse tension rather than inflame the situation there. So I think we should do everything possible to make sure that peace and stability is maintained."
US Ambassador to the United Nations Susan Rice told reporters on Thursday: "We think the Council should respond credibly, I believe it will.
"We have said, and others have said, that the wise thing would be for North Korea to forego this provocative and ill-considered action which is in blatant violation of international law and their international obligations," she said.
The launch will take a three-stage rocket over a sea separating the Korean peninsula from China before releasing a satellite into orbit when the third stage fires over waters near the Philippines.
On Wednesday, North Korea said it was injecting fuel, meaning that the rocket could blast off as early as Thursday, at the start of a five-day window.
Japan's Kyodo news agency reported a government source as saying poor weather meant there was unlikely to be a launch on Thursday.
Ban said he hoped North Korea would become a "responsible member of the international community".
"If and when the DPRK launches what they say is a satellite, or missile, I believe that member states will bring this matter to the Security Council," he said.
