Multiple fake bomb threats against US aircraft in the air

Multiple bomb threats against U.S. aircraft in the air and one on the ground in Philadelphia were made on Tuesday, according to . It was determined that the threat against the plane in Philadelphia was in fact a hoax.

The threats, five in total, were similar to chemical weapon threats against aircraft that were made last week. It was determined that the claims were fake, and there was speculation that the threats could have been made by an ISIS "lone wolf," reported.

Government sources told that none of the threats this morning are credible.

A US Airways flight and its passengers were searched after the plane landed at Philadelphia International Airport Tuesday morning.

The airport confirmed there was an ongoing police investigation after flight 648 from San Diego landed as scheduled in Philly, with 88 passengers and five crew on board.

"The TSA Operations Center in Washington, DC had received a phone threat stating that there was an explosive device on the plane," Philadelphia Police Chief Inspector Joe Sullivan told . "Out of an abundance of caution" the airport declared a bomb threat and moved the plane to a remote area.

The most recent threats come after Homeland Security Secretary Jeh Johnson said he reassigned the acting administrator for the Transportation Security Administration after earlier ordering improved security at U.S. airports.

It followed media reports that checkpoint screeners failed to detect mock explosives and weapons in 95 percent of tests carried out by undercover agents.