The offer of talks, the first since South Korea elected dovish President Moon Jae-In, came as the Red Cross in Seoul proposed a separate meeting to discuss reunions of families separated by the 1950-53 Korean War.
The new data reflects China's attempt to pull off a delicate balancing act between the USA and North Korea, where it wants to prevent the regime collapsing because it worries about what that would mean for regional stability.
About 90 percent of North Korea's exports go to China, and coal has been the single-biggest export item.
Chinese foreign ministry spokesman Geng Shuang hit out on Tuesday against "certain people, talking about the Korean Peninsula nuclear issue, [who] have been exaggerating and giving prominence to the so-called "China responsibility theory".
In response to North Korea's latest missile test, the US and South Korea conducted live-fire bombing exercises along the DMZ, making one wonder who's really provoking whom?More news: Cyber loss potential parallels hurricane risk
North Korea on Friday threatened to take "corresponding measures" if the UN Security Council adopts another sanctions resolution in response to the country's test-launch of an Intercontinental Ballistic Missile, ICBM, on July 4. The last reunions were held in October 2015 at a resort at Mount Kumgang on North Korea's east coast.
The U.S. wants to toughen United Nations sanctions against the North, including restricting oil sales. Previous releases of Chinese customs data showed that China bought the same amount of iron ore in the first five months of this year as it did in all of last year.
The council also said it opposed a military solution to the North Korea problem and kept the door open to dialogue.
"North Korea, one of the world's worst human rights abusers, is continuing to expand its nuclear and ballistic missile threats against the American homeland and our allies", said Rubio.