Russia called on influential parties Friday to facilitate UN experts\' investigation into an alleged use of chemical weapons in Syria. \"We emphatically urge all parties that have the ability to influence the opposition to take steps to help guarantee the fulfillment of the international experts\' mission,\" Foreign Ministry spokesman Alexander Lukashevich said in a statement. He said the Damascus\'s decision to approve a visit by high-ranking UN officials to Syria was an \"indication of a constructive approach.\" The spokesman referred to the upcoming visit by Carla del Ponte, a member of the special independent commission of the UN investigating human rights violations in Syria. A UN team of chemical weapons investigators, led by Swedish expert Ake Sellstrom, had been working in Damascus since Monday. \"We ... maintain constant contact with the Syrian administration, encouraging its constructive interaction with the group of UN experts led by Ake Sellstrom, who are currently in Syria,\" Lukashevich said. Meanwhile, he regretted that \"signals from the opposition, including those of its readiness to ensure the safety and effective work of UN experts on territory controlled by its militants, which is so needed today, are not being heard.\" The spokesman said materials accusing the Syrian troops of using chemical weapons near Damascus were prepared before the incident. \"Increasing amounts of evidence have emerged indicating that this criminal act was of an openly provocative character,\" he said. \"In particular, reports circulating on the Internet said materials about the incident that blame the government were posted several hours prior to the so-called attack.\" The Syrian opposition claimed that President Bashar al-Assad\'s forces killed as many as 1,300 people in chemical weapon attacks in Damascus suburbs on Wednesday, a charge denied by the Syrian government.