Rasmussen congratulated Haidar al-Abadi on his nomination as Iraq's new prime minister.
"This represents an important step in the constitutional process towards the formation of a new government."
According to the Iraqi constitution, Abadi has 30 days from his appointment to form a unity government.
The NATO secretary general echoed a message conveyed by the U.S., that "inclusive government is essential in defeating the Islamic State in Iraq and the Lebant, which represents a threat to the security and stability of the region as a whole."
Abadi was officially nominated to the position of premier by Iraqi President Fouad Massoum on Monday.