An Iraqi coalition is battling its way toward Tikrit for a third day, facing Islamic State snipers and roadside bombs as it flanks the extremist group's strategic stronghold north of Baghdad.
With an estimated 30,000 fighters pressing toward the rebel-held city, the offensive is Iraq's largest to date in an effort to regain control of territory lost to the militants last year.
The Islamic State group on Tuesday claimed an American citizen with the nom de guerre Abu Dawud al-Amriki launched a suicide attack against encroaching Iraqi forces near the city of Samarra, the staging ground where anti-IS forces organized the march on Tikrit. The claim could not be independently verified.
Shi'ite and Kurdish militia members have joined Iraqi troops in the province of Saladin in a highly publicized campaign to storm the provincial capital - and birthplace of executed leader Saddam Hussein - which was overrun by IS militants in June.
Neighboring Iran is also said to have a hand in rolling out the operation, which includes air strikes and ground troops.
Major General Qasem Soleimani, who heads the elite Iranian special forces division known as the Quds Force, joined Iraqi Prime Minister Haider al-Abadi at the start of the offensive earlier this week.
But beyond the tactical support, the extent of Iran's involvement in the battle for Tikrit remains unclear.
A senior U.S. military official confirmed to VOA Pentagon correspondent Carla Babb that Tehran is contributing to the Tikrit offensive.
A U.S.-led international coalition, which is responsible for daily air raids targeting the Islamic State group in Iraq and Syria, has been noticeably absent from the campaign; the military official said that as long as Iran is involved, the United States will stay out of the operation.
A victory in Tikrit would be a geographic stepping stone for Iraqi forces to approach Mosul, Iraq's second-largest city that serves as an IS stronghold and nerve-center.