The campaign to win China's backing for deeper sanctions against North Korea gained in intensity Friday, with the US and South Korean presidents making their case directly to Xi Jinping.

Presidents Barack Obama and Park Geun-Hye spoke to their Chinese counterpart by phone in separate calls to demand punitive measures following a recent nuclear test.

On January 6 Pyongyang detonated what it claimed was a powerful thermonuclear bomb.

The unpredictable hermit state has followed up by threatening to launch a satellite-bearing rocket -- an operation widely seen as a covert ballistic missile test.

The White House and its allies want to respond with a UN resolution that would slap more sanctions on the North.

But they must first win the backing of UN veto power China, which has in the past shielded its neighbor.

Despite Beijing's annoyance with North Korea's nuclear ambitions and its young maverick leader Kim Jong-Un its priority has been to prevent chaos on China's border.

The White House said that Obama and president Xi agreed on the need for a "strong and united international response to North Korea's provocations," including "through an impactful UN Security Council resolution."

But the terse White House statement did not indicate whether that meant agreement on specific steps.

The Obama administration has long pressed China to use its influence with its neighbor, which is heavily dependent on aid from Beijing to keep the population alive.

Xi received a similar message late Friday from Park, who has spent political capital to improve relations with Beijing.

During a 45-minute phone call, "President Park stressed strong and effective resolutions that could force North Korea to change its course must be adopted at the UN Security Council this time," the presidential Blue House said in a press statement.

The North's provocative action posed threats to peace in Northeast Asia and the world, Park said, demanding that "the international community's stern message should quickly lead to action."

"In this context, President Park called for active cooperation from China," which has "leverage with various means" over the North, the statement added.

China's official Xinhua state news agency said Xi stressed China was firmly committed to the denuclearization of the Korean Peninsula and insists on a solution through dialogue and consultation which meets the common interests of Northeast Asian countries.

He expressed hope that "all parties concerned will... deal with the current situation in a sober-minded way," Xinhua reported.

North Korea is already subject to numerous UN sanctions over previous nuclear and rocket tests, but Park said on Thursday its continued provocative behavior showed these had been ineffective.

The only solution, she argued, was to impose sanctions harsh enough "to make it realize that it will not survive unless it gives up its nuclear program."

S. Korea's Park calls for active China cooperation against N. Korea
Seoul (AFP) Feb 5, 2016 - South Korean President Park Geun-Hye on Friday called for China's active cooperation in adopting "strong" sanctions against North Korea, in her first discussions with Chinese leader Xi Jinping since the North's fourth nuclear test last month.

North Korea has said it will launch a satellite-bearing rocket sometime between February 8-25, just weeks after the nuclear test which sparked international condemnation and prompted the United Nations to discuss new sanctions against the communist nation.

During a 45-minute phone call late Friday, "President Park stressed strong and effective resolutions that could force North Korea to change its course must be adopted at the UN Security Council this time", the presidential Blue House said in a press statement.

The North's provocative action posed threats to peace in Northeast Asia and the world, Park said, demanding that "the international community's stern message should quickly lead to action".

"In this context, President Park called for active cooperation from China", which wields a veto power at the UN Security Council and has "leverage with various means" over the North, the statement added.

China's official Xinhua state news agency said Xi stressed China was firmly committed to the denuclearisation of the Korean Peninsula and insists on a solution through dialogue and consultation which meets the common interests of Northeast Asian countries.

He expressed hope that "all parties concerned will... deal with the current situation in a sober-minded way", Xinhua reported.

China is the North's main diplomatic protector and provider of trade and aid, and while ties have become strained over Pyongyang's insistence on pursuing its atomic weapons programme, Beijing has not announced any concrete moves to rein in its neighbour.

UN sanctions prohibit North Korea from any use of ballistic missile technology, and the rocket launch would amount to another major violation of UN Security Council resolutions following January's nuclear test.

The North insists its space programme is purely scientific in nature, but the United States and allies, including South Korea, say its rocket launches are aimed at developing an inter-continental ballistic missile capable of striking the US mainland.

North Korea is already subject to numerous UN sanctions over previous nuclear and rocket tests, but Park said on Thursday its continued provocative behaviour showed these had been ineffective.

The only solution, she argued, was to impose sanctions harsh enough "to make it realise that it will not survive unless it gives up its nuclear programme."