"I hope to see a draft tomorrow perhaps, but you know it's up to the Americans," a diplomat told Reuters on condition of anonymity.
The details of the draft were not immediately available.
China's Foreign Ministry declined to confirm it had reached a deal with the United States.
"We have said many times that China supports an appropriate response from the U.N. Security Council and have also expressed our stance that we oppose North Korea conducting its nuclear test," spokeswoman Hua Chunying told reporters at the regular daily briefing in Beijing.
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"At the same time, we are resolute in believing that the relevant response has to be prudent and moderate, has to prevent an escalation, be conducive to the denuclearization of the Korean peninsula, prevent nuclear proliferation and maintain the peace and stability of Northeast Asia."
Council diplomats have said that they would like to strengthen the provisions in previous sanctions resolutions adopted after North Korea's 2006 and 2009 nuclear tests, above all those related to the inspection and seizure of shipments of banned items and toughening financial restrictions.
The U.N. Security Council strongly condemned North Korea's third nuclear test, on Feb. 12, and vowed to take action against Pyongyang for an act denounced by all major world powers, including ally China.
Pyongyang said at the time that the test was an act of self-defense against "U.S. hostility" and threatened stronger steps if necessary.
In January the Security Council passed a resolution expanding U.N. sanctions against North Korea due to its December rocket launch and warned Pyongyang against further launches or nuclear tests. North Korea responded by threatening a new atomic detonation, which it then carried out the following month.
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North Korea's previous nuclear tests had prompted the Security Council to impose sanctions that included a ban on the import of nuclear and missile technology, an arms embargo and a ban on luxury goods imports.
There are 17 North Korean entities, including banks and trading companies, on the U.N. blacklist, and nine individuals — all linked to North Korea's nuclear and missile programs. U.N. diplomats say many more entities and individuals could be subject to international asset freezes and travel bans.
Beijing has supported all previous sanctions resolutions against Pyongyang but only after working hard to dilute proposed measures in negotiations on the texts. It has been concerned that tougher sanctions could further weaken the North's economy and prompt refugees to flood into China.
