The Islamic State claimed that one of its fighters, a US citizen, carried out a suicide operation against Iraqi forces south of Takrit, AFP reported on Tuesday.
Supporters of the jihadist group alleged that the operation, which they say took place on Monday, occurred near Samarra, just south of Tikrit, in a location that served as a dispatch point for Iraqi troops sent to oust the Islamic State from Tikrit.
The fighter, who allegedly detonated a explosive filled vehicle was identified by the jihadist group as "brother" Abu Dawud al-Amriki, the latter part of his name indicating his country of origin.
Al-Amriki is said to have been targeting a contingent of combatants loyal to Baghdad, killing dozens.
Commanders in the Iraqi military say that their efforts to lay siege to Tikrit have been troubled by the Islamic State group's recourse to guerilla tactics, such as car bombs, roadside explosive devices and sniper fire.