Arab leaders urged dialogue and an end to Syria's bloody crackdown at a landmark summit in Baghdad on Thursday, while Iraq's premier warned that arming rival camps would spark a "proxy war."

Regional leaders approved a resolution calling for an end to the government's crackdown on dissent, for the opposition to unite and for parties to the conflict to launch a "serious national dialogue."

Iraqi Prime Minister Nuri al-Maliki's remarks at the summit highlighted the split in the Arab League.

While hardliners Qatar and Saudi Arabia have called for President Bashar al-Assad to step down and for rebels opposing his regime to be supplied with weapons, others including Iraq have been pushing for a political reconciliation.

Gulf states, apart from Kuwait, largely snubbed the summit, with Riyadh and Doha only sending envoys to the first Arab meet to be held in the Iraqi capital in more than 20 years.

Nine visiting leaders attended the summit of the 22-member Arab League, along with UN chief Ban Ki-moon. Syria, which has been suspended from the pan-Arab body, was not invited.

"Based on our experience in Iraq, the option to arm either side of the conflict will lead to a regional and international proxy war in Syria," Maliki warned in his speech to Arab leaders, adding that "this option will prepare the ground for foreign military intervention in Syria."

Even as the summit was taking place, Syrian security forces assailed rebel strongholds across the country, a day after Assad's regime said it would not abide by any Arab League initiatives.

While regional officials wanted to tackle a wide variety of issues, ranging from the Arab-Israeli conflict to jumpstarting the bloc's economies, the summit was firmly focused on the crisis that has cost thousands of lives in Syria.

In his speech, UN chief Ban Ki-moon called for Syrian authorities to implement UN-Arab League envoy Kofi Annan's peace plan and for an end to the year-long violence ravaging the country.

"It is essential that President Assad put those commitments into immediate effect. The world is waiting for commitments to be translated into action. The key here is implementation. There is no time to waste," he said.

Annan's plan includes a commitment to stop all violence, daily two-hour humanitarian ceasefires and media access to all areas affected by the fighting.

Syrian state news agency SANA said Thursday that Assad had agreed to the plan.

"The acceptance means that there may be a sign of hope, and the Syrian government has to immediately and fully implement the points presented by Mr Kofi Annan," Arab League chief Nabil al-Arabi said at a closing news conference.

Tunisian President Moncef Marzouki, however, told the summit that Damascus was only aiming to prolong the conflict so the regime could "negotiate ... from a position of strength."

"There is no solution except for the president to step down," he said.

A resolution approved by the leaders called on the "Syrian government and all opposition factions to deal positively with the envoy (Annan) by starting serious national dialogue."

It also called on the Syrian opposition "to unify its ranks and prepare ... to enter into serious dialogue" with the regime, while also saying that "the Syrian government should immediately stop all actions of violence and killing."

And it said "the massacre committed by the Syrian military and security forces against civilians in Baba Amr... can be considered crimes (against) humanity," referring to a district of the flashpoint city of Homs in central Syria.

Iraq deployed 100,000 security forces in an effort to prevent attacks on the summit, and officials closed down swathes of roads and mobile networks and shut down the country's airspace.

Last week, Al-Qaeda-claimed attacks nationwide killed 50 people, including three in a car bombing opposite the foreign ministry.

Despite razor-tight security measures for the summit that in effect shut down Baghdad, a mortar round struck near the Iranian embassy on the outskirts of the heavily-fortified Green Zone where the summit was held, a police official said.

The blast caused no casualties but damaged the embassy, according to the official.

The interior ministry said on its website that "we succeeded in maintaining security during the summit," and it thanked "the citizens for their cooperation and patience."

In Washington, US State Department Mark Toner congratulated Iraq on staging the summit.

"All indications are that it has gone well and that Iraq should be proud of what it's been able to accomplish in recent years," Toner told reporters.

"We believe the hosting of this summit is indicative of its positive role in the region and among the community of nations," he said.