"The first batch of Sukhoi Su-25 jets has arrived in Iraqi territory, which will enhance the combat capability of the Iraqi Air Force in eliminating terrorism," the Defense Ministry said.

The aircraft will soon enter service and "change the battle situation," ministry spokesman Mohammed al-Askari told the independent Alsumaria News website.

The Islamic State in Iraq and the Levant (ISIL) militants seized large swathes this month of northern and western Iraq. The Iraqi government said its troops have since wrested back areas from ISIL.

ISIL on Sunday apparently declared a faked self-declared caliphate in Iraq and Syria, in an audio clip on Twitter.

The authenticity of the recording was not immediately confirmed.

State media, citing military sources, reported that the army was pursuing an overall offensive against ISIL.

Government troops were pushing deeper into Tikrit, 140 kilometers north-west of Baghdad, and had "cleansed" most of the city of insurgent forces, Alsumaria said, citing an unnamed security official. "Security forces were able today to tighten their hold on most parts of Tikrit," the official said.

Other security officials said ISIL militants had kidnapped 26 people, mainly security personnel, in the northern province of Salah al-Din.

The abductions were carried out during two overnight raids by ISIL in the town of Sharqat, an official said.

NJF/NJF