But she also shot down hopes that a meeting this week between senior Chinese officials and North Korean leader Kim Jong-Il will produce a quick breakthrough in the crisis sparked by Pyongyang's first test of a nuclear bomb last week.
Rice, who met on Friday with Chinese President Hu Jintao and other leaders as part of a tour of the region, said they were determined to ensure no illicit materials crossed China's long land border with North Korea -- a major conduit for North Korean trade.
"The Chinese made the point to us that they are scrupulous about that land border and intend to be scrupulous about that land border," Rice told reporters accompanying her on the trip.
Tight controls on cargo flows across the 1,400-kilometer (880-mile) border are seen as critical to enforcement of a UN ban on North Korean trade in weapons of mass destruction and related materials and of exports of luxury goods to Pyongyang's elite.
Rice was on a tour to rally support for the UN sanctions that already took her to Japan and South Korea, Washington's two key allies in the region.
China had been very reluctant to clamp trade sanctions on North Korea for fear of weakening the Stalinist regime's already faltering economy, in particular balking at demands it inspect cargo coming from and going to the isolated Stalinist state.
But Rice said the Chinese attitude changed dramatically after Pyongyang carried out its first nuclear test on October 9 and she expressed great confidence that they would fully implement the sanctions resolution for which they voted in the UN Security Council.
"I'm quite sure they didn't undertake a Chapter 7 resolution lightly," she said, referring to the chapter of the UN Charter which imposes mandatory sanctions on states deemed to "threaten international peace and security".
Rice declined to provide details of her talks on just what sanctions China was willing to impose on its troublesome neighbour, stressing she had not come to the region "bringing my own list of what people should do".
But she did discuss the need for China to closely monitor North Korean exports to make sure the cash-strapped regime, which is known for selling weapons on the black market, does not put nuclear material into the wrong hands.
"I think that you will see (Chinese) co-operation on cargo, particularly if there is suspicious cargo," she said.
"Nobody wants to be on the wrong side of this resolution, in other words having something slipping through because you weren't vigilant about enforcing the resolution," she told reporters accompanying her on the four-nation tour.
The top US diplomat said she could not confirm reports that Chinese banks had begun restricting the transfer of funds to North Korea or speculate on whether Beijing could cut down the crucial flow of discount-price oil -- measures that could cripple the Pyongyang regime but which Beijing had hitherto refused to impose.
"Let's just watch what the Chinese do," she said.
Rice also played down media reports that a meeting this week between a top Chinese envoy and Korean leader Kim Jong-Il had produced a breakthrough.
South Korean and Japanese media said Kim indicated to the envoy, Tang Jiaxuan, that North Korea would not carry out another nuclear test.
But when asked about what Tang told her about his talks in Pyongyang, Rice said "there wasn't anything particularly surprising" out of the encounter.
Chinese officials and Rice agreed that their aim was to draw North Korea back into six-party negotiations involving China, Japan, Russia, South Korea and the United States.
Foreign Minister Li said the goal had to be peacefully resolving the crisis "through dialogue and negotiations".
The six-party talks yielded a September 2005 agreement on disarming Pyongyang in exchange for security guarantees and aid, but North Korea pulled out of the process two months later after the US slapped sanctions on a bank accused of money laundering for the regime.
Rice travels on Saturday to Moscow where she is also likely to meet more resistance to tightening the screws on Kim Jong-Il's communist regime.

Copyright AFP (Agence France-Presse), 2006