The leader of the World Trade Organization on Wednesday blamed the U.S. for making it harder for the body to settle trade disputes, in an op-ed for China Daily.

WTO Director-General Roberto Azevedo used his op-ed to warn that "global trade is under threat" due to an escalation of trade restrictions over the last six months. While he didn't directly blame the Trump administration for starting some of the bigger fights, he did blame the U.S. for blocking the appointment of panelists that help resolve trade disputes.

"Despite its effectiveness and the fact that it is in higher demand than ever, the dispute settlement system faces a serious challenge," he wrote in China's state-run paper. "The appointment process for the Appellate Body — the body of adjudicators which hears appeals to dispute cases — is blocked, due to certain concerns held by the US about the body's rulings and procedures."

The decision to block panelists dates back to mid-2016, when the Obama administration objected to the reappointment of a South Korean panelist to the Appellate Body, after disagreeing with some of his decisions.

But Azevedo indicated that position has been taken up by the Trump administration, and warned that without approving new members, the Appellate Body won't be able to function.

"As adjudicators' terms come to an end, we will soon reach the minimum number needed for it to operate," he wrote. "WTO members are ready to sit down and resolve the matter but at the moment this conversation is not advancing. We need real commitment from all sides to break this impasse."

Azevedo used most of his op-ed to lament the use of unilateral trade measures over the last several months. The Trump administration launched many of the major trade fights by imposing tariffs on steel and aluminum imports, and by threatening to walk away from NAFTA.

China and other countries responded by imposing retaliatory tariffs against the United States. It was seen as a widespread violation of the normal WTO process in which countries first have to make their case that a trading partner isn't playing by the rules before imposing tariffs.

The Trump administration has also imposed new tariffs against China to protest China's lack of respect for U.S. intellectual property rights, and for its policy of forced technology transfer. China on Wednesday responded by imposing a new wave of tariffs against the U.S.

"The situation is extremely serious," Azevedo warned. "Reciprocal trade restrictions cannot be the new normal. A continued escalation would risk a major economic impact, threatening jobs and growth in all countries, hitting the poorest the hardest."

[Also read: 'Point of no return' draws closer in U.S.-China trade standoff]