Baghdad, June 30 (RHC)-- The Sunni militant group leading a rebellion against the Iraqi government has declared a Muslim caliphate in the parts of Syria and Iraq under its control.

In a statement, the Islamic State in Iraq and Syria, known as ISIS or ISIL, said it will now be known as the "Islamic State." The group also called on Islamist factions worldwide to pledge allegiance, a potential challenge to its former ally, al-Qaeda.

Iraqi lawmakers are holding a key session on Tuesday to begin selecting a new government. This comes as the Iraqi army has launched a new offensive to re-take the northern city of Tikrit.

Speaking in Geneva, a spokesperson for the United Nations refugee agency said aid officials have been unable to reach tens of thousands of displaced Iraqis.