The United States has condemned a "horrifying" massacre by militants said to have killed hundreds of Iraqi Shia air force recruits in the northern city of Tikrit, urging the country to unite.
Fighters from the Islamic State of Iraq and the Levant (ISIL) have overrun a succession of major towns and cities in the north of Iraq over the last week and are closing on Baghdad.
On Friday, tweets attributed to ISIL claimed the militants had killed 1,700 Shia soldiers as they advanced toward the capital, a figure that has not been independently verified.
"The claim by the Islamic State of Iraq and the Levant that it has massacred 1,700 Iraqi Shia air force recruits in Tikrit is horrifying and a true depiction of the blood lust that these terrorists represent," US State Department spokeswoman Jen Psaki said in a statement.
"While we cannot confirm these reports, one of the primary goals of ISIL is to set fear into the hearts of all Iraqis and drive sectarian division among its people."
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She said US officials "condemn these tactics in the strongest possible terms and stand in solidarity with the Iraqi people against these horrendous and senseless acts of violence".
About 40,000 people have fled Tikrit and Samarra after they came under attack from ISIL militants, according to the International Organisation for Migration.
The latest figure adds to the half a million people the IOM estimates fled Iraq's second city, Mosul, after it was overrun Tuesday.
"Terrorists who can commit such heinous acts are a shared enemy of the United States, Iraq and the international community," Psaki said.
"This underscores the need for Iraqi leaders from across the political spectrum to take steps that will unify the country in the face of this threat."
Secretary of State John Kerry meanwhile made phone calls to his counterparts from Jordan, the United Arab Emirates, Saudi Arabia and Qatar to discuss the ISIL threat in Iraq and neighbouring Syria.
"With each of his counterparts, Secretary Kerry addressed the need to support the Iraqi and Syrian people in confronting terrorists who also pose a threat to nations throughout the region and beyond, including to the United States," a senior State Department official said.
"They also discussed the need for the Iraqi leaders to put aside differences and implement a co-ordinated and effective approach to forge the national unity necessary to move the country forward."
