Gunmen killed five policemen in a checkpoint shooting north of Baghdad on Monday, the deadliest of attacks that left 13 dead, officials said amid a nationwide surge in violence.

Gunmen killed five policemen in a checkpoint shooting north of Baghdad on Monday, the deadliest of attacks that left 13 dead, officials said amid a nationwide surge in violence.

The unrest came days after an Al-Qaeda-linked group claimed responsibility for a spate of car bombings in the capital last week, killing 50.

In Monday's worst attack, gunmen opened fire on a police checkpoint near Tikrit, capital of Salaheddin province, killing the five officers.

Also in Salaheddin, two near simultaneous roadside bombs targeted an army patrol along a main road near the Baiji oil refinery, killing two soldiers and wounding three.

Six people died in violence elsewhere, among them an alleged militant linked to Al-Qaeda and two policemen, in attacks that included a suicide car bombing.

 Iraq has seen a surge in violence since the beginning of 2013, in which nearly 4,000 people have died so far, according to an Agence France Presse tally.