US officials involved in enforcing international sanctions against North Korea expressed optimism Friday that China was willing to cooperate to disrupt financing for Pyongyang's nuclear and missile programmes.

"China is part of the solution and is working with us in a cooperative spirit," Dan Fried, the State Department's sanctions coordinator, told reporters in Beijing.

The latest effort to punish North Korea, UN Security Council Resolution 2094, came in response to its nuclear test last month and after a rocket launch in December.

But previous attempts by the global body to derail Pyongyang's nuclear and missile development have failed.

Fried and David Cohen, the Treasury undersecretary for terrorism and financial intelligence, held talks with Chinese officials on Thursday and Friday, following visits to Tokyo and Seoul earlier in the week.

China, which borders North Korea and has been a key source of trade as well as political and military support for the country for more than six decades, is seen by analysts as the key to making sanctions effective.

Resolution 2094 stands a higher chance of working, Cohen said, citing provisions targeting financial services and cargo shipments supporting the North's nuclear, missile and arms programmes, bulk cash smuggling by Pyongyang, and the role of its diplomats.

"We've heard nothing but the strong intention to implement the Security Council resolution," said Cohen. "And we fully expect to work very cooperatively with the Chinese in the robust implementation of that resolution."

But the officials declined to offer any concrete examples of Chinese action so far to shake up the North's nuclear and weapons financing.

Asked about Japanese media reports that Chinese banks have begun to halt some remittances to the North, Cohen said he had seen them and was "very interested" in what will happen given the "fair amount" of financial ties between the countries.

"So we are hopeful that the Chinese banks and the Chinese regulators will take heed of the Security Council resolution and have every confidence, frankly, that that will occur," he said.

North Korean-Chinese trade nearly tripled in the five years to 2011 to $5.6 billion, figures compiled by the South Korean government show, underlining Pyongyang's deepening dependence on Beijing.

China accounted for 70.1 percent of the North's entire external trade of $8.0 billion, up from 41.7 percent in 2007, South Korea's statistics agency said in December.

The trip by Fried and Cohen to Beijing comes just after one by US Treasury Secretary Jacob Lew, and ahead of a visit by new Secretary of State John Kerry.

Fried acknowledged the challenge of whether sanctions would influence North Korea's behaviour. "The possibility for further provocation unfortunately exists," he said.