An influential Sunni Muslim cleric said on Monday that only dialogue could solve Iraq's crisis, sounding a conciliatory note on the threat posed by Sunni Islamist insurgents that could further polarise the Middle East along sectarian lines.

Fighters from the radical Islamic State of Iraq and the Levant (ISIL) have seized a swathe of northern Iraqi towns, as well as border posts with Syria, in a thrust towards Baghdad, stunning the country's Shi'ite Muslim-led central government.

Sunni Saudi Arabia has blamed Iraqi Prime Minister Nuri al-Maliki, saying his rule had incurred Iraqi Sunnis' wrath, and hinted that Shi'ite Iran should not enter the fray in Iraq against the militants.

"There's no doubt that Sunnis all around the world are being repressed but even more so in Iraq under the Shi'ite leadership," cleric Youssef al-Qaradawi told a news conference in the Qatari capital Doha.

"I have called for bridging the differences between Sunnis and Shi'ites, and in the past I travelled to Iran to initiate dialogue...," said the Egyptian-born Qaradawi, who is revered by millions of Sunni Muslims worldwide.

"Iraq always had Sunnis and Shi'ites and we ask them not to mention sects in this war and work together."

Qaradawi added that not only ISIL, but also other Sunni groups including members of former Iraqi President Saddam Hussein's Ba'ath party were leading the fight against Maliki.

A Doha-based Islamist group Qaradawi leads called last week on Arab and Muslim countries to protect the Sunnis in Iraq but condemned "terrorist" groups it said violate Muslim principles.

Ali al-Qaradaghi, a cleric serving under Qaradawi at the International Union of Muslim Scholars, said the extremists represented only a small fraction of Maliki's Sunni opponents.

"Not more than 10 per cent of the Sunnis leading this war are from ISIL ... and once Sunnis get their rights there will be no presence of ISIL in Iraq," Qaradaghi said.

Qaradawi's outspoken support for the Muslim Brotherhood movement in the region has contributed to an unprecedented diplomatic rift between Qatar and its Gulf allies, who withdrew their ambassadors from Doha earlier this year.

Qatar's backing of the Brotherhood and shelter for Qaradawi has stoked tension with other Gulf monarchies, who oppose them.

Since the dispute began, Qaradawi has refrained from delivering Friday sermons, but on the sidelines of Monday's conference he told Reuters that he would return following Ramadan - which is expected to start next week.

"I stopped the sermons to relieve a bit of the pressure on Qatar. As you can see, the ambassadors haven't come back yet, but I will resume after Ramadan ends, God willing," he added.-Reuters