North Korea conducted its fifth and biggest nuclear test on Friday and said it had mastered the ability to mount a warhead on a ballistic missile, ratcheting up a threat that rivals and the United Nations have been powerless to contain.

The blast, on the 68th anniversary of North Korea's founding, drew a fresh wave of global condemnation. The US said it would work with partners to impose new sanctions, and called on China to use its influence - as North Korea's main ally - to pressure Pyongyang to end its nuclear program.

Under 32-year-old third-generation leader Kim Jong Un, North Korea has sped up development of its nuclear and missile programs, despite U.N. sanctions that were tightened in March and have further isolated the impoverished country.

The United Nations Security Council denounced North Korea's decision to carry out the test and said it would begin work immediately on a resolution. The US, Britain and France pushed for the 15-member body to impose new sanctions.

UN Secretary General Ban Ki-Moon urged the group to remain united and take action that would "urgently break this accelerating spiral of escalation."

US President Barack Obama said after speaking by telephone with South Korean President Park Geun-hye and with Japanese Prime Minister Shinzo Abe that they had agreed to work with the Security Council and other powers to vigorously enforce existing measures against North Korea and to take "additional significant steps, including new sanctions."

But Russian Foreign Minister Sergei Lavrov said it may take more than additional sanctions to resolve the crisis. That diverged from calls by the United States, Japan and South Korea to escalate pressure on the North, signaling it may prove a challenge for the Security Council to come to an agreement on new sanctions.

"The current situation shows that diplomats should be more creative than just responding by sanctions, sanctions and sanctions again on any aggravation of the situation," Lavrov told a news conference in Geneva. "It is too early to bury the six-party talks. We should look for ways that would allow us to resume them."

The so-called six-party talks aimed at ending the North's nuclear program involving the US, Russia, Japan, South Korea, China, and North Korea have been defunct since 2008.

Secretary of State John Kerry said the US had repeatedly offered talks to North Korea, but Pyongyang had to accept de-nuclearization, which it had refused to do.

"We have made overture after overture to the dictator of North Korea," he said, adding that he ultimately hoped for a similar outcome as in the nuclear talks in Iran.

China said it was resolutely opposed to the test but Chinese Foreign Ministry spokeswoman Hua Chunying would not be drawn on whether China would support tougher sanctions against its neighbor.

On Saturday, the influential Chinese state-run tabloid the Global Times said North Korea was wrong in thinking building nuclear weapons would provide it more security or prestige in the world.

"Owning nuclear weapons won't ensure North Korea's political security," it said in an editorial. "On the contrary, it is poison that is slowly suffocating the country."

Beijing has also repeatedly expressed anger since the US and South Korea decided in July to deploy the Terminal High Altitude Area Defense (THAAD) anti-missile system in the South.

China says that THAAD is a threat to its own security and will do nothing to bring North Korea back to the negotiating table on its nuclear program.

“Washington and Seoul, in particular, should sincerely rethink their decision to install THAAD on the peninsula and review their other strategic mistakes that have prompted Pyongyang to make the wrong steps,” Wang Junsheng, a researcher in Asia Pacific strategy at the government think tank, the Chinese Academy of Social Sciences, told the official China Daily in a piece published on Saturday.

Still, US Defense Secretary Ash Carter singled out the role he said China should play. "It's China's responsibility," he told a news conference during a visit to Norway. "China has and shares an important responsibility for this development and has an important responsibility to reverse it."

South Korea's Park said late on Friday Kim was "mentally out of control," blind to all warnings from the world and neighbors as he sought to maintain power. "The patience of the international community has come to the limit," she said.

North Korea, which labels the South and the US as its main enemies, said its "scientists and technicians carried out a nuclear explosion test for the judgment of the power of a nuclear warhead," according to its official KCNA news agency.

It said the test proved North Korea was capable of mounting a nuclear warhead on a medium-range ballistic missile, which it last tested on Monday when Obama and other world leaders were gathered in China for a G20 summit.

Pyongyang's claims of being able to miniaturize a nuclear warhead have never been independently verified.

Preliminary data collected by the Vienna-based Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which monitors nuclear tests around the world, indicated the magnitude - around 5 - of the seismic event detected in North Korea on Friday was greater than a previous one in January.

Jeffrey Lewis of the California-based Middlebury Institute of International Studies said the highest estimates of seismic magnitude suggested this was North Korea's most powerful nuclear test so far.

He said the seismic magnitude and surface level indicated a blast with a 20- to 30-kilotonne yield or its largest to date.

Such a yield would make this test larger than the nuclear bomb dropped by the United States on the Japanese city of Hiroshima in World War Two, which exploded with an energy of about 15 kilotonnes.

South Korea's military put the force of the blast at 10 kilotonnes, which would still be the North's most powerful nuclear blast to date.

"The important thing is, that five tests in, they now have a lot of nuclear test experience. They aren't a backwards state any more," Lewis said.-Reuters