The United States and many of its allies Tuesday announced the expulsion of Syrian diplomats in a coordinated move to step up pressure on Damascus after the weekend’s mass killings of civilians.Western countries appeared convinced that the Syrian military was behind the massive assaults on the town of Houla that killed 108 civilians and injured 300 more, despite repeated denials by the Syrian government. Analysts say the Houla killings could serve as a "perfect pretext” for the West to take military action against Syria, but this was not possible in the near future given the current conditions on the ground. The only viable option to end violence in Syria, they say, remains the implementation of the six-point peace plan raised by joint UN-Arab League envoy Kofi Annan.Speaking in Damascus after a meeting with Syrian President Bashar al-Assad on Tuesday, Annan expressed satisfaction with Damascus’ promise to conduct a thorough probe into the Houla killings and voiced appreciation for its cooperation in the deployment of UN monitors. He urged al-Assad to "take bold steps” immediately to create momentum for the implementation of the six-point peace plan and asked the armed opposition to cease violence.The former UN secretary general noted that both the Syrian government and the opposition had not "completely” abided by the plan, saying more serious efforts were needed from both sides. Meanwhile, al-Assad said the success of the peace plan depended on a cessation of attacks by "terrorists,” who were receiving weapons from "related countries.”Russian Foreign Minister Sergei Lavrov told Annan in a phone conversation Tuesday that the implementation of the plan had become "more relevant” in the current situation amid calls by the opposition for outside military intervention. The Syrian government and the opposition should "sit down and start political dialogue instead of killing each other,” he said.Before talking to Annan, Lavrov told reporters that the domestic turmoil in Syria had already affected neighboring Lebanon and could cast a shadow over the entire region.