Venezuela accused the United States on Thursday of denying President Nicolas Maduro’s plane permission to enter U.S. airspace — a claim that a State Department official denied.

Foreign Minister Elias Jaua said U.S. officials have blocked plans for Maduro’s presidential plane to fly through Puerto Rican airspace on the way to China.

He described the move as an aggression and called for an explanation from the U.S. State Department.

A senior State Department official told CNN that Jaua’s claim was untrue, saying that the Venezuelans have, in fact, been approved to clear U.S. airspace.

In remarks broadcast on state television, Maduro called the situation “a serious offense.”

The Venezuelan president vowed to take action, adding that the United States had also denied visas for several members of his country’s delegation scheduled to attend the U.N. General Assembly in New York.

The State Department official also called the visa issue untrue, saying the United States had approved them.

Maduro is scheduled to travel to China on Saturday. Jaua said officials were evaluating alternate routes so that the trip could continue as scheduled.