President Donald Trump escalated his threats against the World Health Organization over its handling of the coronavirus pandemic, saying he would permanently cut U.S. funding if it does not make sweeping reforms.

He said that the international agency must demonstrate “independence from China,” according to a letter, which the president posted on Twitter late Monday.

“If the World Health Organization does not commit to major substantive improvements within the next 30 days, I will make my temporary freeze of United States funding to the World Health Organization permanent and reconsider our membership in the organization,” Trump wrote in the letter to Director General Tedros Adhanom Ghebreyesus.

In a tweet accompanying a copy of the letter, Trump called it “self-explanatory.”

The president announced on April 14 he would temporarily suspend U.S. funding to the WHO, accusing the group of being too supportive of China.