Iraq's state television Al-Iraqiya television said on Monday that government forces - backed by allied Shiite and Sunni fighters - were attacking the city of Tikrit, with the support of artillery and airstrikes by Iraqi fighter jets.

Militants were reported to have been dislodged from some areas outside the city, but there were no further details.

Forces in northern Iraq's autonomous Kurdish region are also making gains against the IS. Similarly, in Syria, Kurdish fighters recently ran the group out of Kobani, a city on the Turkish-Syrian border.

'Last chance'

The offensive came hours after Prime Minister Haider al-Abadi called on Sunni tribal fighters to abandon the extremist group and promised them a pardon.

"I call on all those who were misled and made mistakes in the past to lay down their arms today. This may be the last chance," Abadi said in Samarra.

After announcing the attack on Sunday, al-Abadi urged forces going into Tikrit to spare the lives of civilians.

"The priority we gave to the armed forces and all the forces taking part alongside them is to preserve the security of citizens," al-Abadi told reporters.

On social media, he called "for utmost care in protecting civilian lives and property."

Christians beheaded

Tikrit, some 130 kilometers (80 miles) north of Baghdad, fell into the hands of IS last summer along with the country's second-largest city of Mosul and other areas in Sunni heartland.

The IS offensive also saw parts of neighboring Syria captured. The terrorist group has killed minorities in Syria and Iraq who do not profess allegiance to its self-proclaimed "caliphate," most recently beheading 21 Egyptian Coptic Christians in Libya.

ksb/jr (AFP, AP)