The head of an international mission to destroy Damascus's chemical arsenal arrived Monday in Syria, where the regime pressed on with deadly strikes despite a flurry of diplomatic efforts to organise peace talks.

"Today, the Special Coordinator, Ms Sigrid Kaag arrived in Damascus," to head up a joint mission of the United Nations and the Hague-based Organisation for the Prohibition of Chemical Weapons.

The Dutch UN official leads a team tasked with inspecting more than 20 sites by the end of the month and destroying Syria's chemical stockpiles by mid-2014 under a US-Russian deal.

Meanwhile, US Secretary of State John Kerry was meeting Arab League representatives in Paris ahead of a Tuesday meeting in London of the opposition and its Western and Arab backers.

UN-Arab League envoy Lakhdar Brahimi told reporters in Baghdad that all countries "with interests and influence in the Syrian affair must participate" in the Geneva 2 peace conference.

Iraqi Foreign Minister Hoshyar Zebari told the same news conference that "everyone is now convinced that (a) political and peaceful solution to the Syrian crisis is the available option" for "the interest of the Syrian people".

On Sunday Brahimi said, during a visit to Cairo, that he hoped the talks would be held next month, but warned they cannot go ahead without the attendance of a "credible opposition".

The veteran troubleshooter has said he will also travel to Qatar, Turkey, Iran, Syria and then Geneva for talks with Russian and US representatives.

A pro-regime daily in Syria said he was expected this week in Damascus, where he came under heavy criticism from the regime for suggesting a transitional government after his last visit in 2012.

Washington and Moscow have been trying to organise the conference on the heels of the deal they reached for the destruction of Syria's chemical weapons.

But the opposition has been fiercely critical of the agreement -- which averted US strikes on the regime following a sarin gas attack in August that killed hundreds of people -- and at least one major faction, the Syrian National Council (SNC), has already refused to go to Geneva.

The opposition has also demanded that President Bashar al-Assad step down as part of any agreement, while the regime has insisted his exit is not on the table.

The National Coalition umbrella opposition group, which includes the SNC, on Monday said it had postponed internal meetings to early November, as it weighs whether to attend the Geneva talks.

Originally set for this week, the group had aimed to discuss and reach a common position on the proposed talks, but Tuesday's conference in London of the Friends of Syria countries that support the rebellion prompted the postponement.

Even if the Coalition attends the Geneva meeting, it is unclear whether it can enforce any agreement, after dozens of rebel brigades in recent weeks rejected the umbrella group.

The Geneva initiative was first announced last year, but it has been repeatedly postponed over opposition objections and a dispute over which countries, including Iran, should participate.

As diplomats wrangled over the proposed talks, government forces killed a rebel commander, Lieutenant Colonel Yasser Abbud, during clashes at Tafas, in the southern province of Daraa, said sources on both sides.

Daraa is the birthplace of an uprising that erupted in March 2011 and flared into a civil war that has killed tens of thousands.

News of the commander's death came as regime forces attempted to blunt a rebel offensive around the town of Mleha, southeast of Damascus, said the Syrian Observatory for Human Rights.

Elsewhere, regime troops pressed their onslaught on the besieged town of Moadamiyet al-Sham southwest of the capital, with fierce clashes between government and rebel troops on the outskirts of the town, the Observatory said.

Moadamiyet al-Sham has been besieged by regime forces for months, with thousands of civilians trapped inside and running desperately low on food and medicine, according to UN officials and residents.

Thirty-one months into Syria's conflict, the army is pushing hard to secure Damascus by trying to crush rebel-held pockets on its outskirts.

Four rockets were also launched from Syria into the eastern Lebanese town of Hermel, a stronghold of the powerful Hezbollah movement that is fighting alongside Assad's forces in their bid to crush the rebellion.