US-led coalition warplanes have launched their first airstrikes against Islamic State of Iraq and the Levant (ISIL) targets in Tikrit, in a boost to Iraqi forces fighting alongside Iran-backed militia on the ground.

A US defence official, speaking on condition of anonymity, said on Wednesday that American warplanes and aircraft from allied nations were striking up to a dozen targets in the northern Iraqi city, the Reuters news agency reported.

A second US official stressed that Washington in no way would coordinate with the Iranian-backed militia or seek to empower them in Iraq, even if those fighters might share the same narrow tactical objective as Iraqi forces in Tikrit.

In language that appeared to intentionally omit the Iranian-backed militia, Lieutenant General James Terry, the senior US commander of the US-led coalition, said the strikes were aimed at enabling "Iraqi forces under Iraqi command".

"These strikes are intended to destroy ISIL strongholds with precision, thereby saving innocent Iraqi lives while minimising collateral damage to infrastructure," Terry said.

'Last page of operations'

Iraqi Prime Minister Haider al-Abadi said Iraqi forces would prevail with the support of "friendly" countries and the international coalition, including arms, training and aerial support.

"We have opened the last page of the operations," Abadi said on state television.

It has been carrying out strikes elsewhere in Iraq since August.

As coalition aircraft entered the fray, Iraqi forces shelled ISIL-held positions in Tikrit, resuming an offensive that had stalled for almost two weeks. 

"Military operations in Tikrit started at around 9pm local time by pounding ISIL positions with artillery, mortars and Katyusha rockets," said provincial council member Hadi al-Khazraji.

More than 20,000 troops and allied paramilitary groups have been taking part in the offensive and have suffered heavy casualties on the edge of the city, 160km north of Baghdad.

The Iraqi military had lobbied for US-led coalition airstrikes while Iran backed paramilitary forces opposed such a move. One militia leader, Hadi al-Amiri, boasted three weeks ago that his men had been making advances for months without relying on US air power.

Source: Reuters