Kofi Annan met top Iranian officials Tuesday before flying to Iraq, as he sought the help of key regional players in shoring up his tattered peace plan for Syria after meeting President Bashar al-Assad.
The UN and Arab League peace envoy underlined Tehran's importance in international efforts to stem the bloodshed, following talks with Iran's Foreign Minister Ali Akbar Salehi.
"Iran can play a positive role," Annan said, adding that he would continue to work with the Iranian leadership to resolve the crisis, which monitors say has cost more than 17,000 lives.
"There is a risk that the situation in Syria gets out of hand and spreads to the region," Annan told a joint news conference with Salehi, who hailed the envoy's "neutrality" and reiterated Iranian support for his mission.
Annan then flew to Baghdad for talks with Prime Minister Nuri al-Maliki on the Syria conflict, a government official.
The former UN chief's Middle East trip follows a meeting of world powers in Geneva late last month -- to which Iran, Damascus's staunchest regional ally, was not invited -- to salvage his peace initiative.
A plan was agreed in Geneva for a political transition in Syria, which did not make an explicit call for Assad to quit, although the West and the opposition made clear it saw no role for him in a unity government.
After meeting Assad on Monday, the former UN secretary general said he had agreed with the Syrian president on a new political "approach" to ending the crisis in Syria that he would put to the rebels.
"We discussed the need to end the violence and ways and means of doing so. We agreed an approach which I will share with the armed opposition," Annan said in Damascus, before flying to Tehran, where he also met Iran's top security official Saeed Jalili.
The opposition Syrian National Council (SNC) had slammed Annan's decision to meet Assad, saying thousands of people have been killed despite an April ceasefire.
Deadly violence on the ground showed no sign no abating on Tuesday.
The army rained shells down on the rebel-held central town of Rastan as violence killed 13 people across the country, according to the Syrian Observatory for Human Rights.
"We have many wounded, and there are no doctors here, only two dentists. We can't do anything for the wounded. It's tragic," an activist in Rastan told AFP via Skype.
Of those killed on Tuesday, seven were civilians, four were soldiers and two were rebels, the Observatory said, noting that 98 people were killed nationwide on Monday, including 34 soldiers, after reporting a similar toll on Sunday.
Russia said on Tuesday that it wanted to host new meeting of foreign powers on the Syria crisis but stressed that the talks should not decide Assad's fate.
Deputy Foreign Minister Mikhail Bogdanov also said the attempt in Geneva to save Annan's peace plan needed to be continued with the involvement of countries such as Iran, which both Washington and European powers strongly oppose.
But the SNC said that its priority was to "work for the fall of the Assad regime and all its symbols," insisting there could be no political transition until the embattled president's departure.
The opposition coalition's new leader Abdel Basset Sayda is due to travel to Moscow on Wednesday at the invitation of the Russian foreign ministry, the SNC said.
Annan, whose observers in Syria have been grounded because of escalating violence, admitted in remarks published by French newspaper Le Monde ahead of his Damascus trip that his peace blueprint has so far foundered.
He has previously expressed frustration that while Moscow and Iran are mentioned by some as stumbling blocks to peace, "little is said about other countries which send arms, money, and have a presence on the ground."
Russia is sending a flotilla of six warships led by an anti-submarine destroyer to its naval base at Syria's port of Tartus, the Interfax news agency reported on Tuesday, citing a military source.
The source said the flotilla's deployment in the Mediterranean would last until the end of September and "was not linked to the escalation of the situation in Syria."
Moscow arms export officials said on Monday that Russia will not supply new weapons to its Arab ally Syria while fighting there continues, while stressing that old contracts would be fulfilled.
France on Tuesday became the latest country to condemn fighting on the Lebanese-Syrian border, after a senior Lebanese security official said shells fired from Syria hit northern Lebanon.
Syrian state news agency SANA, citing a source in central Homs province which neighbors Lebanon, later said Syrian troops foiled attempts by "armed terrorist groups" to infiltrate from Lebanon during the night.
The incident came just two days after border clashes in which two girls were killed and several other people wounded.