Iraq's new Prime Minister Haider al-Abadi has urged his countrymen to unite in the face of dangerous challenges and cautioned that the road ahead would be tough. 

On his Facebook page, Abadi on Friday said he would not make unrealistic promises but he encouraged Iraqis to work together to strengthen the country, which is being wracked by sectarian violence. 

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Nouri al-Maliki on Thursday stepped down as the country’s prime minister, bowing to huge domestic and international pressure. He voiced support for his designated successor Abadi, a fellow member of the Shia Dawa party.

On Friday, Iraq's most influential cleric, Grand Ayatollah Ali al-Sistani, also threw his weight behind the new prime minister and said the transition was a rare opportunity to resolve political and security crises.

Underscoring the urgency of containing a sectarian conflict fuelled by fighters from the Islamic State group, Sistani urged the military to hoist only Iraq's flag to avoid factionalism.

Sistani, in a weekly sermon delivered through a spokesman in the sacred Shia city of Karbala, called on the political blocs in parliament to be "responsible" and cooperate with the prime minister-designate.

Last week, he blamed Iraqi politicians for the country’s biggest crisis since the fall of Saddam Hussein in 2003, saying they are motivated by self-interest.

The stepping down of Maliki was swiftly welcomed by the US and the UN.

"Today, Iraqis took another major step forward in uniting their country," US National Security Advisor Susan Rice said.

UN Secretary-General Ban Ki-moon called for the swift formation of "an inclusive, broad-based government ready to immediately tackle these pressing issues".

The decision of Maliki, 64, to turn the page on eight years in power was welcomed at home as well, but some said little will change.

"Maliki stepping down is a positive move to end the crisis," Baghdad resident Salah Abu al-Qassem told the AFP news agency.

But the 38-year-old added that Abadi and Maliki are "both from same school".

Sunnis 'marginalised'

"I do not believe that changing the government will be a solution for Iraq," said Mohammed Majid, 53, a resident of the city of Samarra, north of the capital.

"We, the Sunnis, have been marginalised for 10 years by the Dawa party," he said.

Maliki, who rose from anonymous exile to become a powerful ruler, said he was stepping aside to "facilitate the progress of the political process and the formation of the new government".

While he defended his record at the helm, critics say his divisive policies have alienated and radicalised the Sunni minority, most of whose heartland was overrun by fighters from the Islamic State in June.

The self-declared jihadist group has since declared a "caliphate" straddling Syria and Iraq, hunted down religious minorities, destroyed holy sites and seized the country's largest dam and several oil fields.

The fighters’ advance has also displaced hundreds of thousands of people and posed an immediate existential threat to the world's seventh oil producer by de facto redrawing its borders along ethnic and sectarian lines.

Iraqi forces folded when Islamic State forces moved in and while the Kurdish peshmerga initially fared better, the US arms that retreating federal troops left behind made the self-declared jihadists a formidable foe.

Source: Agencies