An unverified audio message was received at multiple air traffic controllers in New York, warning of a terror attack on the Capitol building on Wednesday when the US Congress meets to confirm Joe Biden as the President.

The audio message, which was received on restricted channels on Monday, said a plane will crash into the US Capitol as Congress meet is underway. US Congress will meet on Wednesday, January 6, to formally declare Biden as the next President, ahead of the January 20 inauguration.

The threat has not been assessed as a credible one but top agencies including the FBI are investigating the breach of air traffic protocols. "The FBI and FAA are looking into a breach of air traffic control frequencies after a threat was made about flying a plane into the Capitol tomorrow," CBS News tweeted.

Congress
US Congress Lars Di Scenza / Wikipedia Commons

The Federal Aviation Administration said it was working "closely with federal law enforcement and national security partners on any reported security threats that may impact aviation safety'. The Pentagon and other federal agencies were also informed about the voice recording received at the airports.

The message referred to slain Iranian general Qassem Soleimani, the number two in the Iranian power structure, who was killed in a US air strike in Baghdad exactly a year ago.

Around the anniversary of the assassination of Soleimani, Iran has ratcheted up rhetoric over retribution and revenge. On Tuesday, Tehran moved Interpol, seeking a red corner notice against President Donald Trump and two dozen American officials. "The Islamic Republic of Iran is very seriously following up on pursuing and punishing those who ordered and executed this crime," judiciary spokesman Gholamhossein Esmaili said.

Qasem Soleimani
Qasem Soleimani, Quds Force commander Wikimedia Commons

The Interpol had rejected a similar request made by Iran in June. The Trump administration responded to Iran's saber-rattling by announcing fresh sanctions against Tehran.

The US earlier dispatched B-52 bombers to the Persian Gulf after Iran stepped up verbal aggression. Trump also decided to reverse a plan to order the return of the USS Nimitz from the Persian Gulf region.

The US-Iran tensions remained high over the week, with Tehran saying it was resuming the processing of uranium to 20 percent enrichment level.

Soleimani, 63, and Abu Mahdi al-Muhandis, deputy head of Iraq's Hashd al-Shaabi, were killed on January 3, when the US drones blew up his convoy outside the Baghdad International Airport.

Soleimani had reportedly flown in from Lebanon or Syria and was heading out of the airport when the Donald Trump-ordered attack took place. Pentagon confirmed the mission, while top officials in Tehran, including the supreme leader Ayatollah Khamenei, vowed revenge.

General Soleimani headed the Quds Force of the Iranian Revolutionary Guards Corps (IRGC). The Quds Force is the powerful external operations wing of the IRGC. Soleimani has been at the helm of the Quds Force since 1998. He had wielded influence across the wider Middle East and was instrumental in strengthening Shia militias from Lebanon to Iraq. He also played a stellar role in propping up Syrian President Bashar Al Assad.