China is preparing to deliver a crushing blow to the weak North Korean economy.

It is suspending all coal imports from North Korea, the Ministry of Commerce said Saturday, without going into specifics as to why it was taking action.

Coal exports are a primary source of income for the reclusive state. Following North Korea’s fourth nuclear test in February last year, the United Nations Security Council passed UNSC Resolution 2270, which placed restrictions on North Korea’s coal exports but made exceptions through the “livelihood purposes” clause. China has been accused of exploiting this loophole to continue importing North Korean coal in order to reduce international pressure on Pyongyang.

China agreed to reduce its coal imports from North Korea last April, yet by August, coal imports had surged. In August, China imported 2.47 million tons of coal from the North. In 2016, China imported 22.48 million tons of coal, a year-on-year increase of 14.5 percent.

After the North conducted its fifth nuclear test in September last year, the UNSC passed UNSC Resolution 2321, which put a cap on North Korean coal exports, reducing its annual coal export revenue by an estimated $700 million. While the resolution does not cut off coal exports completely, the move reduces North Korea’s $3 billion in annual export earnings by roughly 25 percent.

Now, China has decided to suspend all coal imports from North Korea from Feb. 19 until Dec. 31, a move that should further reduce the funds available for militarization and weapons development.

The decision follows a meeting between Secretary of State Rex Tillerson and Foreign Minister Wang Yi Friday on the sidelines of the G20 foreign ministers meeting in Bonn, Germany. During their meeting, Tillerson “highlighted the increasing threat posed by North Korea’s nuclear and missile programs and urged China to use all available tools to moderate North Korea’s destabilizing behavior,” Department of State spokesman Mark Toner said in a statement.

It is unclear whether China’s decision is a result of Tillerson’s calls for China to rein in North Korea.

Beijing’s patience with Pyongyang is growing thin. North Korea tested a new surface-to-surface medium-range ballistic missile last Sunday in clear violation of international regulations. Last year, the North conducted two nuclear tests and over two dozen missile tests, all of which China officially condemned.

After last week’s ballistic missile test, China reportedly rejected a shipment of North Korean coal at a port in Wenzhou. China upped the ante this Saturday by rejecting all shipments going forward.

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