In their biggest offensive against "Islamic State" (IS) fighters so far, Iraqi government forces and Iran-backed militia have entered the town of al-Dour on Tikrit's outskirts.

Al-Dour is where executed former Iraqi dictator Saddam Hussein was found hiding in 2003. Tikrit was his home city.

Hadi al-Amiri, leader of the largest Shiite militia group taking part in the operation, said al-Dour had been "totally liberated" and that the advance on al-Alam, another key town north of Tikrit, would take place on Saturday.

The Iraqi army, joined by thousands of Shiite militiamen backed and advised by Iran, is five days into the advance on Tikrit 140 km (80 miles) northwest of the Iraqi capital, Baghdad, on the Tigris River.

Army officials said on Friday that they had captured a farm to the east of Tikrit that belonged to Saddam's deputy Ezzat Ibrahim al-Douri. He is now a prominent ally of the jihadist fighters. He is also the only member of the former regime still at large following the 2003 US led invasion of Iraq.

Commander of Iran's Revolutionary Guards elite Quds Force, Qassem Soleimani was seen in Iraq this week and is assumed to have assisted in supervision of the offensive.

The United States has said it has played no role in the Tikrit offensive. Its air campaign against IS fighters in both Iraq and Syria is ongoing.

IS militants were reported to have set fire to oil wells near Tikrit and to have laid mines and explosive devices throughout the region to obstruct the offensive against them.

The move on Tikrit is a key element in Iraq's campaign to regain control of territory held by IS. The army, backed by Shiite militia and Kurdish peshmerga fighters, has not yet retaken any city held by IS. There have been seven months of air strikes by the US-led coalition, together with weapons supplies and strategic support from Iran.

Thousands of Tikrit residents have fled their city, saying they fear the militia more than IS. There are fears that Shiite militia will seek revenge for the 1,700 Iraqi soldiers captured and killed by IS at the Speicher military base just outside Tikrit last June.

Iraq's senior Shiite cleric Ayatollah Ali al-Sistani has spoken out against any attempts at vengeance against civilians. "Be protectors for the weak and aid them in getting to a safe haven," he said in a Friday sermon.

The offensive is seen as a key test of Iraq's forces, especially if they are to continue their offensive on to Mosul, the largest city under IS control.

jm/sms (Reuters, AP, AFP)