MANILA, Philippines – A bomb threat believed to have come from within the Ninoy Aquino International Airport complex sent police teams sweeping through a US-bound jumbo jet before dawn Saturday, nearly five hours before its scheduled flight.

Delta Airlines flight DL-172 bound for New York with a stopover in Narita, Japan, took off after a slight delay at 8:21 a.m. after police declared the Boeing 747 clear of any threat, a report from the Manila International Airport Authority said.

The plane was originally scheduled for takeoff at 7:55 a.m. Passengers boarded the aircraft without incident, but additional bomb-sniffing dogs were placed at the Delta Airlines’ check-in counter, departure gate and the airport ramp.

Information from the MIAA said personnel manning baggage conveyors at NAIA Terminal 1′s arrival hall received a call at 3 a.m. Saturday saying the Delta aircraft “will explode at 5 a.m.”

The caller spoke in Filipino and used a local line, indicating that the call was made from within the NAIA complex, said an MIAA source who requested anonimity for lack of authority to speak on the matter. A check of MIAA’s phone system showed that no such call came through the trunkline.

The caller made two calls, 10 minutes apart, said the source, who was at NAIA 1 at the time and was privy to police response to the threat.

The call came just as two Delta planes, both parked at the NAIA ramp overnight, were being readied for their early-morning flights.

Apart from Flight 172, Delta’s Manila-Nagoya-Detroit flight DL 630, also a 747 that was set for an earlier flight, was also at the tarmac and already open for check-in at the time.

Teams from the Philippine National Police and the separate Airport Police Department deployed K9 units to inspect both aircraft. The sweep took around an hour and the inspection cleared the two planes of any threat.

MIAA said the threat did not cause any disruption to the operations at the terminal or alarm the passengers.

An investigation was underway to trace the caller.