BAGHDAD, Oct. 21 (Xinhua) -- Four policemen were killed and five others wounded on Monday in an attack by Islamic State (IS) militants in Iraq's central province of Salahudin, a police officer said.

The attack took place in the evening when IS militants attacked a police force tasked with protecting Allas oilfield, some 40 km east of the provincial capital Tikrit, Khalaf Mohammed Hussein from the force told Xinhua.

A fierce clash erupted between the two sides as IS militants tried to exploit the bad weather of rain and wind, but the attackers withdrew as reinforcements arrived, Hussein said.

Allas oilfield is producing some 20,000 barrels per day of crude oil, Hussein added.

In 2014, IS militants took control of Allas and nearby Ajil oilfields and extracted large amounts of oil to finance its operations. But the two oilfields were freed by the Iraqi forces in March 2015.

The security situation in Iraq was dramatically improved after Iraqi security forces fully defeated the extremist IS militants across the country late in 2017.

IS remnants, however, have since melted in urban areas or resorted to deserts and rugged areas as safe havens, carrying out frequent guerilla attacks against security forces and civilians.