The helicopter took off from Clark in Pampanga province for the two-hour training exercise but failed to return as scheduled

MANILA: A recently delivered Philippine assault helicopter crashed during a night training exercise north of Manila, killing all six air force personnel on board, officials said Thursday.

Defence Secretary Delfin Lorenzana said it was still unknown why the S-70i Blackhawk helicopter carrying three pilots and three crewmen crashed Wednesday night near Clark Air Base, a former American military base that is now a bustling industrial and recreation complex.

"No survivors have been found," air force spokesman Lt Col Maynard Mariano said, adding that similar Blackhawks have been grounded amid an investigation into the crash.

"We grieve for the loss."

The helicopter took off from Clark in Pampanga province for the two-hour training exercise but failed to return as scheduled.

A search and rescue team later found the wreckage, Mariano said without elaborating.

The Defence Department finalized a deal to acquire 16 of the Blackhawks for USD 241 million in 2019 under a military program to modernize one of Asia's most ill-equipped and underfunded militaries.

Aside from fighting decades-long communist and Muslim insurgencies, the military has been under pressure to acquire more equipment and weapons to defend its territories and claimed areas in the disputed South China Sea.

The helicopter that crashed was among six that were delivered in November.

The rest of the Blackhawks will be received by the military within the year, Mariano said.