NEW YORK • The US and China are locked in negotiations over curbing North Korea's energy trade in response to its fifth nuclear test last month, according to four diplomats from United Nations Security Council countries with direct knowledge of the talks.

The world's two biggest economies - both of which can veto any resolution - are discussing restrictions on North Korea's trade in coal, iron ore and crude oil, according to the diplomats, who asked not to be named because the discussions are private.

Other nations are also considering separate sanctions against North Korea once the Security Council acts, the diplomats said.

The US and its allies are seeking to further tighten sanctions against Mr Kim Jong Un's regime to prod him into abandoning the pursuit of nuclear weapons, which has intensified in recent years, with the latest test occurring on Sept 9.

The measures stand little chance of success without support from China, which has kept its neighbor from collapsing to avoid both a humanitarian crisis and the presence of American and South Korean troops on its border.

"The US wants to strangle North Korea, but is asking China to be the executioner," said Mr Shi Yongming, an associate research fellow at the Foreign Ministry-run China Institute of International Studies.

In a statement to Bloomberg News on Tuesday, China's foreign ministry confirmed that it is in "negotiations with relevant parties" on North Korea without responding to questions on details.

China accounts for more than 70 per cent of North Korea's trade and provides most of its food and energy supplies, according to the Council on Foreign Relations.

In March, the UN passed its toughest sanctions yet against Mr Kim's regime, but a loophole allows it to trade goods needed for "livelihood" or emergencies.

BLOOMBERG