BEIJING — In a sign of growing concern about North Korea’s nuclear ambitions, China published a long list on Tuesday of equipment and chemical substances to be banned from export to North Korea for fear they could be used in adding to its increasingly sophisticated nuclear weapons programs.

If put into place, the export controls would be some of the strongest steps taken by China, the North’s closest ally, to try to limit the country’s nuclear programs. The announcement indicates that China is now following through on some United Nations Security Council sanctions it approved months ago, according to a noted American arms expert.

The list of banned items was released amid a flurry of reports suggesting that North Korea is accelerating its two nuclear weapons programs. Two weeks ago, new satellite photographs showed that North Korea might be resuming production of plutonium at its newly reconstructed nuclear reactor at Yongbyon. And this week, two American arms experts reported that North Korea appeared to have learned to produce its own crucial components for uranium enrichment.

The move also comes less than a week after China made an unsuccessful attempt to revive talks aimed at persuading the North to give up its nuclear capabilities. The United States continues to resist restarting the talks, which North Korea has used in the past to extract concessions without making long-term changes to its nuclear program.