TIKRIT/FALLUJA, Iraq (Reuters) - At least one person was killed and 14 wounded when a bus carrying workers at a small oil refinery in northern Iraq was blown up by an improvised explosive device, police said.

The bus was at the Siniya refinery, near Iraq’s largest oil refinery of Baiji in the predominantly Sunni Salahuddin province, when it exploded, Baiji police said on Saturday.

Separately, three civilians and a policeman were injured when a parked car exploded in a market area in Falluja within the western, also Sunni, Anbar province, security sources said.

No group has claimed responsibility for either attack, but Islamic State militants are active in both provinces.

Iraqi forces declared victory over the hardline Sunni Islamist group in December after retaking all the territory it held in a four year war, but its fighters are waging a guerrilla-style insurgency.

Security sources said the attack in Falluja was the first since Iraqi forces retook the city from the militants in 2016.

It came only after Popular Mobilisation Forces (PMF), an umbrella network of mostly Shi’ite militias, started operating within the city, residents and tribal leaders said.

PMF forces have long been stationed at checkpoints around the city and in the entire province but had not entered the city proper before.