BEIRUT (Reuters/AFP) - Kofi Annan arrived in Damascus on Sunday evening for talks with President Bashar al-Assad, his spokesman said, a day after the international peace envoy admitted that his peace plan had so far failed to end 16 months of bloodshed.Syria's navy fired live missiles from ships and helicopters over the weekend, state media said on Sunday, in an exercise aiming at demonstrating its ability to "defend Syria's shores against any possible aggression".US Secretary of State Hillary Clinton said Syrian opposition forces were growing more effective and the sooner the violence ended, the better were the chances of sparing Syria's government from a "catastrophic assault" by rebel fighters.Syrian television aired video of a variety of missiles being fired from launchers on land and from ships and showed Syrian Defence Minister Dawud Abdallah Rahijia in attendance."Naval Forces conducted an operational live fire exercise on Saturday, using missiles launched from the sea and coast, helicopters and missile boats, simulating a scenario of repelling a sudden attack from the sea," Syrian news agency SANA said, adding that manoeuvres would continue for several days.Clinton appeared to be referring to the possibility of Syrian rebels launching such an assault on state institutions rather than to any outside intervention."There is no doubt that the opposition is getting more effective in their defence of themselves and in going on the offence against the Syrian military and the Syrian government's militias. So, the future .... should be abundantly clear to those who support the Assad regime," Clinton added. "The sand is running out of the hour glass."Annan himself has said his UN-backed mission has so far failed to halt the bloodshed, while stressing that Russia and Iran must not be sidelined from peace efforts."Russia wields influence but I am not sure that the events will be determined by Russia alone... Iran is an actor. It has to be part of the solution. It has influence and we cannot ignore it," Annan told France's Le Monde daily.Syrian President Bashar Al-Assad accused the United States of assisting "gangs" to destabilise his country, in a rare interview with a western television channel to be aired on Sunday.The United States is "part of the conflict. They offer the umbrella and political support to those gangs to... destabilise Syria," Assad told German public broadcaster ARD.According to a text of the interview, carried out on July 5 and due to be broadcast later Sunday, Assad also refused to step down, saying he was staying put to deal with the "challenge" Syria is facing."The president shouldn't run away from challenge and we have a national challenge now in Syria," said Assad in English."The president shouldn't escape the situation, but from the other side you can stay as president, stay in this position only when you have the public support," he added.Iranian President Mahmoud Ahmadinejad has accused the United States and its allies of opposing Assad's regime with the goal of dominating the Middle East and propping up Israel.Iran's deputy foreign minister Hossein Amir Abdollahian said on Sunday in Jordan that any attack on Syria would be "stupid" and "catastrophic.""Military action Syria is unlikely and if this happens it would be stupid. Syria can defend itself without Iran's help. Any non-political solution would bring catastrophe to the entire region," he said.UN Secretary General Ban Ki-moon, who also attended the Tokyo conference, renewed his call on the UN Security Council for collective action to pressure Syria to stop the violence. "President Assad must understand that things cannot continue as they are. Fundamental change is needed," Ban said.On Sunday at least 46 people, including 20 civilians, were killed in violence across Syria, the Observatory said. Syrian forces attempted to storm the rebel strongholds of Qusayr and Rastan in the central province of Homs, the watchdog said."Fierce clashes took place before dawn between regime forces and rebels in the vicinity of Qusayr, accompanied by heavy shelling on Qusayr and neighbouring villages as the regime tried to regain control," Observatory director Rami Abdel Rahman told AFP.In Rastan, "the army carried out shelling in an attempt to storm the city and clashed with fighters from the rebel combat battalions, forcing the government troops to retreat," he said.Both towns have been outside regime control for months and are rebel strongholds.