(CNN) China has agreed to reclassify fentanyl as a "controlled substance," in what the White House is calling a "wonderful humanitarian gesture" after the much-anticipated talks Saturday between US President Donald Trump and Chinese President Xi Jinping in Buenos Aires, Argentina.

In a statement, China's Foreign Ministry said China has "decided to schedule the entire category of fentanyl-type substances as controlled substances, and start the process of revising relevant laws and regulations."

China and the United States have "agreed to take active measures to strengthen cooperation on law enforcement and narcotics control," including the control of fentanyl-type substances, it said.

The new designation for the synthetic opioid drug means people in China who sell fentanyl to the US "will be subject to China's maximum penalty under the law," according to a statement from the White House.

Trump and Xi met Saturday for dinner on the sidelines of the G20 summit in Buenos Aires.

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