ALGIERS (Reuters) - Algerian counter-terrorism forces on Sunday searched around the eastern city of Constantine after a policeman was killed in a rare urban attack by gunmen believed to be from a local Islamic State affiliate, a security source said.

Bombings and attacks are rare since Algeria ended its 1990s civil war with Islamists that killed 200,000 people. But Al Qaeda in the Islamic Maghreb and small brigades of Islamic State affiliates are still active, mostly in mountainous areas or the remote south near the country’s borders with Niger and Libya.

Three gunmen shot the officer in a restaurant in a northern district of Constantine late on Friday, the security source said. Witnesses have been shown images of potential suspects in the attack, the source said.

“According to witnesses, these individuals went straight to the victim as he was eating and shot him and then took his service weapon,” another security official told El Watan, a daily French-language newspaper.

Authorities have made no official statement.

In March, police shot dead a would-be suicide bomber in a small town east of the capital, Algiers. The last suicide attack in Algeria was in 2011 in the same town, when a militant tried to drive a bomb-packed truck into a police station, injuring 29 people.

Al Qaeda in the Islamic Maghreb in March also claimed a rocket attack on an Algerian gas plant, operated by BP and Statoil with state-owned Sonatrach, though it caused no casualties or notable damage.

In August, Algerian forces said they had cleared out Islamic State-affiliated militants, known as Jund al-Khilafa or Soldiers of the Caliphate, from the mountains east of Algiers, two years after they kidnapped and beheaded a French tourist in the former al Qaeda stronghold.