China’s trade with North Korea shrank by more than half last month, as Beijing implements United Nations sanctions against Kim Jong Un’s nuclear weapons program.

The value of Chinese goods exported to North Korea last month fell 23 percent year on year, according to data released Friday by China’s General Administration of Customs. Imports from the country also plunged 82 percent in December. All told, trade between the two sides fell almost 51 percent during the month.

In 2017 as a whole, China’s overall trade with North Korea declined by more than 10 percent to about $5 billion, as U.S. President Donald Trump secured Beijing’s backing for four escalating rounds of sanctions. The U.S. sees cutting off North Korea’s economic ties with China—the country’s dominant trading partner—as essential to forcing Kim back to the negotiating table.

“We’ve been very pleased that China has certainly given much fuller implementation,” Brian Hook, director of policy planning for U.S. Secretary of State Rex Tillerson, told reporters in Washington on Thursday. “They have closed some sanctions gaps. They are doing a better job of implementing the UN Security Council resolutions.”

After North Korea tested its most powerful nuclear device yet and launched missiles capable of reaching the U.S., the UN Security Council imposed a series of sanctions restricting oil imports and cutting off about 90 percent of its export revenue. The latest round passed last month.

North Korea’s first talks with South Korea in more than two years turned tense Tuesday, after representatives of President Moon Jae-in proposed discussions with Kim about giving up his nuclear weapons program. While China says they support a denuclearized Korean Peninsula, Beijing has resisted sanctions so harsh that they might cause widespread suffering or topple Kim’s regime.