DAMASCUS  - Kofi Annan warned on Tuesday that Syria's deadly conflict could spread across the region as he held talks in Iran and Iraq aimed at shoring up support for his tattered peace plan.A day after meeting President Bashar al-Assad in Damascus, the UN-Arab League peace envoy had talks in Tehran and Baghdad amid new bloodshed in Syria where more than 17,000 people have reportedly been killed since March 2011.Washington insisted Tuesday that it sees no role for Iran in resolving the conflict in Syria, in an implicit rebuff to UN envoy Kofi Annan's outreach to Tehran."I don't think anybody with a straight face could argue that Iran has had a positive impact on developments in Syria," White House spokesman Jay Carney told reporters aboard US President Barack Obama's jet Air Force One.In Tehran, he stressed that the Islamic republic, Syria's staunchest regional ally, has a key role to play, and also sought help from Iraq, another neighbour of Syria. "Iran can play a positive role," Annan said after meeting Iranian Foreign Minister Ali Akbar Salehi."There is a risk that the situation in Syria gets out of hand and spreads to the region," Annan told a news conference with Salehi, who hailed the envoy's "neutrality" and reiterated Iranian support for his mission.Annan then flew to Baghdad where, he said, he had "very good discussions" with Prime Minister Nuri al-Maliki and later told reporters he would brief the UN Security Council on Wednesday. "And I'm sure the council will take appropriate action, including the future of UNSMIS, the monitors on the ground, as their mandate comes up on the 21st of July," Annan said of unarmed UN military observers deployed in Syria.Deadly violence showed no sign no abating on Tuesday. The army rained shells down on the rebel-held central town of Rastan as violence killed at least 21 people nationwide, the Syrian Observatory for Human Rights said. "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, at least nine were civilians, four soldiers and four rebels, the Observatory said, noting that 98 people were killed on Monday, including 34 soldiers.Among the dead was Syrian Arab Red Crescent staffer Khaled Khaffaji, shot by unknown gunmen overnight in the eastern province of Deir Ezzor.Dr Abdul Rahman al-Attar, president of the organisation, said people were "devastated" by the death.Russia said on Tuesday that it wanted to host a 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.Russia has sent a flotilla of six warships 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 would last until the end of September and "was not linked to the escalation of the situation in Syria."Lebanon, meanwhile, began reinforcing its border with Syria following a series of deadly attacks, a military spokesman said in Beirut.Syrian troops traded gunfire with men overnight in the border area and shells fell inside Lebanon, wounding civilians, the army said, just two days after border clashes killed two girls.Syrian state news agency SANA confirmed the violence and said troops foiled attempts by "armed terrorist groups" to infiltrate from Lebanon during the night.