BAGHDAD (Reuters) - Thousands of Iraqi soldiers and Shi'ite militiamen sought to seal off Islamic State fighters in Tikrit and nearby towns on Tuesday, the second day of Iraq's biggest offensive yet against a stronghold of the radical Sunni Islamist militants.
Iranian military commander Qassem Soleimani, who has helped coordinate Baghdad's counter-attacks against Islamic State since it seized much of northern Iraq
in June, was overseeing at least part of the operation, witnesses told Reuters.
His presence on the frontline highlights neighboring Iran's influence over the Shi'ite fighters who have been key to containing the militants in Iraq.
In contrast the US-led air coalition which has been attacking Islamic State across Iraq andSyria has not yet played a role in Tikrit, the Pentagon said on Monday, perhaps in part because of the high-level Iranian presence.
Iraqi military officials said security forces backed by the Shi'ite militia known as Hashid Shaabi (Popular Mobilisation) units were advancing gradually, their progress slowed by roadside bombs and snipers.
They have yet to enter Tikrit, best known as the hometown of executed former president Saddam Hussein, or the nearby Tigris river town of al-Dour, which officials describe as a major center for the Islamic State fighters.
On the southern flank of the offensive, army and police officials said government forces moving north from the city of Samarra could launch an attack on al-Dour later on Tuesday.
Soleimani, head of the Iranian Revolutionary Guards Quds Force, was directing operations on the eastern flank from a village about 55 km (35 miles) from Tikrit called Albu Rayash, captured from Islamic State two days ago.
With him were two Iraqi Shi'ite paramilitary leaders: the leader of the Hashid Shaabi, Abu Mahdi al-Mohandis, and Hadi al-Amiri who leads the Badr Organisation, a powerful Shi'ite militia.
"(Soleimani) was standing on top of a hill pointing with his hands toward the areas where Islamic State are still operating," said a witness who was accompanying security forces near Albu Rayash.
The offensive is the biggest military operation in the Salahuddin region north of Baghdad since last summer, when Islamic State fighters killed hundreds of Iraq army soldiers who had abandoned their military base at Camp Speicher outside Tikrit.
Several Shi'ite Hashid Shaabi fighters have described this week's campaign as revenge for the Speicher killings. Prime Minister Haider al-Abadi has urged them to protect civilians in Salahuddin, a mainly Sunni Muslim province.
The drive follows several failed attempts to push the militants out of Tikrit. Since Islamic State declared a caliphate last year in territories under its control in Iraq and Syria
, Iraqi forces have not managed to recapture and control a single city.
But months of US-led air strikes, backed up by the Shi'ite militias, Kurdish peshmerga fighters and Iraqi soldiers, have contained Islamic State in Iraq and pushed it back from around Baghdad, the Kurdish north, and the eastern province of Diyala.
The Tikrit battle will have a major impact on plans to move further north and recapture Mosul, the largest city under Islamic State rule.
If the offensive stalls, it will complicate and delay a move on Mosul. A quick victory would give Baghdad momentum, but any retribution against local Sunnis would imperil efforts to win over Mosul's mainly Sunni population.
To the west of Mosul, Islamic State fighters attacked Kurdish forces in the town of Sinjar on Monday, a senior peshmerga source said. Nine peshmerga and 45 militants were killed in the fighting, which began with a suicide car bomb in the Nasr quarter of the town.
Islamic State "want to show people they can still attack and inflict losses on the peshmerga", the source said. Kurdish forces currently control around 30 percent of the town of Sinjar, as well as the hills to the north and the mountain overlooking it.