Iraqi forces have captured another district and some oil fields outside of Tikrit, but were met with fierce resistance as they tried to advance into the city controlled by the Islamic State of Iraq and the Levant (ISIL), according to state television.

Iraqiya TV reported on Monday that government troops, backed by Shia volunteer fighters and Iraqi air strikes, have entered the district of al-Alam, said to be the last stop before Tikrit, 18km northeast.

The ground troops were composed of joint forces from Tigris, Samarra and Salaheddin, as well as militiamen and tribal fighers from Salaheddin.

Iraqiya TV also reported that the government forces and their allied militia have taken control of the oil wells in al-Ojail oil field northeast of Tikrit.

But ISIL fighters, who controlled al-Alam, have reportedly set fire to some oil fields to confuse government forces, and shield themselves from attack by helicopter.

Control of oil fields has always been an ISIL hallmark, even when its fighters lack the technical expertise to operate them at full capacity.

The extent of the damage to the oil fields was not immediately clear.

In June 2014, ISIL took over al-Ojail, which produces an estimated 25,000 barrels per day of crude oil that used to be shipped to the Kirkuk refinery to the northeast, as well as 4 million cubic metres of gas per day piped to the government-controlled Kirkuk power station.

Crucial battle

The battle over Tikrit is crucial for Iraqi forces in their advance towards Mosul, Iraq's second largest city.

Tikrit also serves as an important hub because it is on the main highway leading to Baghdad.

The army, backed by Shia militias are based just 30km southeast of the city, in al-Dour, which was retaken by government forces last week.

Capturing al-Alam and al-Dour cuts off vital ISIL supply routes.

Iraqi troops are also standing by further out, in Samarra and Beiji, as well as outside the town of Garma in Anbar Province.

Government forces are also trying to push forward to the city of Fallujah, which is just 10km away. Fallujah has been under ISIL control for several months.

Meanwhile, Kurdish forces are also attacking ISIL positions around the oil-rich city of Kirkuk in northern Iraq.

The fighters have been advancing from several areas to the west of the city, seizing villages as they go.

The city itself is under Kurdish control but ISIL still controls some areas nearby.

Peshmerga forces said they have killed 100 ISIL fighters, but Al Jazeera could not independently verify the report.

Source: Al Jazeera and agencies