Thursday's directive from Vice President Khader al Khuzaei, acting on behalf of the President, came amid calls for political action to tackle sectarian tensions that have fueled the crisis.

In a televised speech, Prime Minister Nuri al-Maliki vowed to stick to the timeline to create a new government while accusing Sunnis of "coordinating" the crisis.

Al-Maliki accused Sunnis of collaborating with the militant group Islamic State in Iraq and Syria, or ISIS, and slammed the call to have a national salvation government that would remove him from power.

He also appealed to his Shia constituency by saying he is adhering to the wishes of Shiite religious leader Ali Sistani, who called for volunteers to support the Iraqi army and government.

Many have accused al-Malaki of marginalizing Iraq's Sunni and Kurd minorities in favor of his fellow Shiites.

U.S. Secretary of State John Kerry on Wednesday played down al-Maliki's rejection of a salvation government, saying it wasn't something the United States had talked to him about specifically.

To the contrary, he said, al-Maliki is committed to the electoral process and creation of a new government that the United States has supported.

"And he committed to moving forward with the constitutional processes of government formation, and that is precisely what the United States was encouraging," Kerry said. "He also called on all Iraqis to put aside their differences, to unite in their efforts against terrorism."

After talks in Paris on Thursday with his French counterpart, Laurent Fabius, Kerry said the two agreed that they want to see the formation of a government in Iraq "as rapidly as possible that represents unity for the country."

The pair are also deeply concerned about the challenge of Syria, he said.

Fabius said that ISIS had shown "terrible ferocity and brutality" and that Iraq must unite to combat it.

"It's a necessity not only for Iraq but the whole region. Because it's a menace for Iraq, for the region, for Europe and the United States as well," he said.

UK Foreign Secretary William Hague, on a visit to Baghdad on Thursday, also urged the swift formation of an inclusive government, saying Iraqi political leaders must put sectarian division aside.

"The Iraqi state is facing an existential threat, with huge ramifications for the future stability and freedom of this country," he said. "The single most important factor that will determine whether or not Iraq overcomes this challenge is political unity."

Hague said this would be the focus of his discussions with al-Maliki and Kurdish regional leader Masoud Barzani.