BAGHDAD — Iraqi troops and Shiite militias battled the Islamic State group Tuesday south of the militant-held city of Tikrit, though roadside bombs and suicide attacks slowed their advance on Saddam Hussein’s hometown.

The battle for Tikrit, a strategic city along the Tigris River, likely will be won or lost on allied Iraqi forces’ ability to counter the extremists’ bombs. Such explosives were a mainstay of al-Qaida in Iraq, the Islamic State group’s predecessor, as it fought American forces following their 2003 invasion of the country.

“Tikrit has been besieged from three directions, from the north, west and south, but what has remained only from the eastern side,” said Brig. Gen. Saad Maan Ibrahim, an Interior Ministry spokesman. “The explosive experts were able to tackle so many bombs and car bombs.”

Ibrahim offered no specifics, though previous reports suggest extremists of the Islamic State group, which holds both a third of Iraq and neighboring Syria in its self-declared caliphate, have littered major roadways and routes with mines. Such mines allow the extremists to slow any ground advance and require painstaking clearing operations before troops can safely move through.

Suicide bombings also aid the militants in weakening Iraqi forces and have been used extensively in its failed campaign for the Syrian border town of Kobani. Already, a militant website affiliated with the Islamic State group has said an American jihadi carried out a suicide attack on with truck bomb on the outskirts of nearby Samarra targeting Iraqi forces and Shiite militiamen, identifying him by the nom de guerre of Abu Dawoud al-Amriki without elaborating.