At least 54 policemen, including 20 officers and 34 conscripts, were killed when a raid on a militant hideout southwest of Cairo escalated into an all-out firefight, authorities said on Saturday, in one of the single deadliest attacks by militants against Egyptian security forces in recent years.

The officials said the exchange of fire began late Friday in the al-Wahat Al Bahriya area in Giza province, about 135 km southwest of Cairo, reported AP.

The firefight began when security forces acting on intelligence moved against a militants' hideout in the area.

Backed by armored personnel carriers and led by senior counterterrorism officers, the police contingent drew fire and rocket-propelled grenades, stated the report citing senior officials.

The officials said what happened next is not clear, but indications suggest that the force ran out of ammunition and that the militants captured several policemen and later killed them. One officer managed to escape in his armored vehicle, they added.

The officials said the police force appeared to have fallen into a carefully planned ambush set up by the militants. The death toll could increase, they added, speaking on condition of anonymity because they were not authorized to brief media.

Those killed included two police brigadier-generals, a colonel and 10 lieutenant colonels, said the AP report.

The last time Egypt's security forces suffered such a heavy loss of life was in July 2015 when militants from the extremist Islamic State group carried out a series of coordinated attacks, including suicide bombings in the Sinai peninsula, killing at least 50.

An official statement issued Saturday said Friday's incident would be investigated, suggesting that the heavy death toll may have been partially caused by incompetence, intelligence failures or lack of coordination.

The officials said prosecutors will look into whether the police's counterterrorism agents failed to inform the military of the operation or include them.

No militant group immediately claimed responsiby for the attack.