An attack by suicide bombers in the Iraqi city of Tikrit killed at least 31 people and injured at least 42, army and police officers said on Wednesday.

A police lieutenant colonel said the attack began when three militants opened fire in central Tikrit on Tuesday night. They later blew themselves up inside homes in the area.

There was no immediate claim of responsibility for the attack, but the Islamic State jihadist group carries out frequent suicide bombings targeting Iraqi civilians and security forces.

The Islamic State seized Tikrit during a lightning offensive that overran large areas north and west of Baghdad in the summer of 2014, but Iraqi forces recaptured it the following year.

Iraqi forces are now battling to retake west Mosul — the country's last city in which the jihadists hold significant ground.

But the jihadists still hold other areas in western Iraq and eastern Syria, and they will remain able to carry out deadly bombings even if all areas under their control are recaptured.