The Federal Bureau of Investigation launched an investigation after U.S. air traffic controllers intercepted a radio communication threatening to crash an aircraft into the U.S. Capitol on Wednesday as legislators were formalizing the November presidential election result, CBS and other news organizations reported.

The anonymous message using a digital voice said the act would be carried out to "avenge" the murder of Iran military general Qasem Soleimani.

"We're flying a plane into the Capitol on WednesdaySoleimani will be avenged," the voice said, according to air traffic controllers in New York, reports said.

Soleimani was killed in a U.S. drone attack last year. He was regarded as the architect of Iran's foreign policy.

The threat was made on the anniversary of the Iranian commander's death.

It is not known who sent the message and federal officials reportedly don't believe the threat was reliable. But top officials at the Pentagon and other government agencies were briefed Tuesday, reports said.

The threat is being examined by the U.S. Federal Aviation Administration for violation of frequencies in U.S. aviation communication protocols.

The frequency breach is concerning because it could disrupt instructions pilots receive, aviation authorities said.

A representative for the administration said the administration is "working closely with federal law enforcement and national security partners on any reported security threats that may impact aviation safety," Insider quoted the officials as saying in a statement.