Gunmen killed three police officers at a checkpoint in the Suez Canal city of Ismailia, the local security directorate said on Saturday.
The attack late on Friday was carried out by two armed men on motorbikes who sprayed the checkpoint with gunfire. One attacker was killed by police and the second fled.
Police are searching for the second attacker.
Unconfirmed reports said that a fourth person was killed.
No group has claimed responsibility for the attack, which bore the hallmarks of operations by ISIS militants who have been fighting the government for years in the north-eastern corner of the Sinai Peninsula on the border with Israel and the Gaza Strip.
Attacks by the Sinai militants were mainly targeted at security forces, minority Christians, residents suspected of collaborating with the military and police or tribesmen openly loyal to the government.
Friday's attack was the deadliest to be publicised since May, when at least 11 Egyptian soldiers were killed in a militant attack on a water pumping station east of the Suez Canal.
The frequency of ISIS attacks has decreased since February 2018, when the military launched a large-scale operation in Sinai, parts of the Nile Delta and the desert border with Libya to the west.