Three Egyptian policemen were killed when masked men attacked a checkpoint in the Nile delta city of Mansoura, security sources said.
No group has claimed responsibility. Al Qaeda-linked militants have stepped up attacks on soldiers and police since the army toppled Islamist President Mohamed Mursi in July.
The majority of the attacks have been carried out in the largely lawless Sinai region, although militants have on occasion extended their campaign into major cities.
Three men in a car and one on a motorcycle approached the checkpoint before dawn and fired at the policemen "to make sure that they were dead", a security source in Mansoura said, speaking on condition of anonymity.
"This is another attack in the series of terrorist attacks against the police," he said. He did not specify who had carried out the attack. State-run newspaper Al-Ahram reported that 60 bullet casings were found at the site.
In Qalyoubiya, another city in the Nile Delta province, a prosecutor ordered the arrest of 16 people suspected of forming a "terrorist cell" for their involvement in the failed assassination attempt on the interior minister in September.
A Sinai-based militant group claimed that attack and released a video saying a former army major had carried out the suicide bombing.
The army-backed interim government says it is fighting a war on terror, and makes no distinction between the Sinai-based militants it calls "terrorists" and ousted president Mursi's Muslim Brotherhood.
Since Mursi's ouster, the state has launched a fierce security crackdown on the Brotherhood, killing hundreds of members, arresting more than two thousand.
The Brotherhood, Egypt's oldest and biggest Islamist group, denies any links with violent activity.
