Iraq launches major assault to retake Tikrit from IS

Kirkuk/Iraq: Some 30,000 Iraqi troops and militia backed by aircraft pounded jihadists in and around Tikrit in the biggest offensive yet to retake one of the Islamic State group's main strongholds.

Government forces have battled their way north for months, notching up key victories against IS, but Tikrit has been their toughest target yet, with the jihadists having resisted them several times.

Commanders voiced hope the operation, launched Monday, would be a step towards the recapture of Mosul, the jihadists' main hub in Iraq, although a US envoy leading an international coalition against IS said no timeline should be imposed.

"The army, federal police, Popular Mobilisation (volunteer) units, and the sons of Salaheddin's tribes are performing the duties of liberation in the largest operation against Daesh since June," said a senior army officer on the ground, using an Arabic acronym for IS.

"We are certain of victory... but the operation is not easy," the officer told AFP.

The operation to retake Tikrit began early Monday after being announced by Prime Minister Haider al-Abadi the previous evening.

Military sources said warplanes were involved, but the Pentagon said they excluded those of the US-led coalition fighting IS.

It was unclear whether Iranian planes were involved, however. Both Iraqi and Iranian media said Qassem Soleimani -- the commander of the Al-Quds Force covert operations unit of Tehran's elite Revolutionary Guards -- was in Salaheddin province, of which Tikrit is the capital, to help coordinate operations.

Hadi al-Ameri, the Popular Mobilisation units' powerful commander, on Saturday urged Tikrit residents to leave their homes within 48 hours so government forces could "wrap up the battle of the revenge for Speicher".

Speicher is a military base near Tikrit from which hundreds of new, mostly Shiite, recruits were kidnapped before being murdered execution-style in the early days of the IS offensive that swept through much of the Sunni Arab heartland north and west of Baghdad in June.

Shiite militias in particular have vowed to avenge the murders, sparking fears of mass killings against Sunnis if Tikrit were to be recaptured.