BEIJING (AP) — China announced Monday it will cut off imports of North Korean coal, iron ore and other key goods in three weeks under U.N. sanctions imposed over the North's nuclear program.

China, the isolated North's main trading partner, has been reluctant to push leader Kim Jong Un's regime too hard for fear it might collapse. But Beijing is increasingly frustrated with Pyongyang and joined in approving a U.N. Security Council ban on Aug. 5 on coal and other key goods.

The Chinese customs agency said it will stop processing imports of North Korean coal, iron and lead ores and fish at midnight on Sept. 5.

The latest sanctions are intended to block exports valued at more than $1 billion — a significant loss to total exports valued at $3 billion last year.