Washington: A United Airlines flight was stuck on the tarmac for hours in Denver following a suspected bomb threat, prompting authorities to evacuate passengers after the aircraft turned back before take-off, according to US media reports.

Flight 2408, scheduled to depart from Denver to Washington, had reached the runway at around 6:15 pm local time when the incident unfolded. Reports said a suspected bomb threat triggered the delay, forcing the aircraft to halt operations and return, after which passengers were evacuated as a precaution.

The development comes amid a separate security scare involving another United Airlines flight over the weekend. On Sunday, a flight travelling from Chicago to New York City was forced to divert to Pittsburgh International Airport following reports of a “possible security issue,” according to CBS News.

The Federal Aviation Administration confirmed that United Flight 2092 landed safely at approximately 11:45 am local time on Saturday after the crew raised the alarm. The FBI Pittsburgh said it was aware of “a reported threat” in a social media update, though details about the nature of the threat were not disclosed.

The aircraft, a Boeing 737 carrying 159 passengers and six crew members, had been en route from Chicago O'Hare International Airport to LaGuardia Airport.

In a statement to CBS News, the airline said the diversion was due to a “potential security concern” and confirmed that passengers “evacuated the aircraft via slides.”

Following the landing, local authorities launched a full-scale security response. A representative of the Allegheny County Airport Authority said the county police bomb squad and K-9 units screened the aircraft “with negative results,” after which the plane was cleared.