Russia said on Friday it had told Syria to cooperate with UN experts investigating reports of a deadly chemical weapons attack, and called on rebels to allow access to the area. Foreign Minister Sergei Lavrov told US counterpart John Kerry in a phone call that immediately after the reports first emerged about the attack Wednesday, the \"Russian side called on the Syrian government to cooperate with the UN chemical experts,\" the foreign ministry said in a statement. \"It is now up to the opposition to ensure safe access for the mission to the site of the alleged incident,\" it added. It said both Lavrov and Kerry agreed on the need for an \"objective investigation\" into what happened. \"Common interest was expressed in an objective investigation by a UN expert mission, which is currently in the country, in connection with the reports about the possible use of chemical weapons in a Damascus suburb,\" the statement said. The Syrian opposition said this week the Damascus regime used chemical weapons near the capital in an attack that killed hundreds of people. Harrowing footage distributed by activists showing unconscious children, people foaming around the mouth and doctors apparently giving them oxygen to help them breathe has triggered revulsion around the world. The opposition National Coalition says more than 1,300 people were killed. The United Nations formally asked Syria to authorise UN experts currently on a mission in Syria to probe the allegations. Russia, which supported the Damascus regime throughout the conflict, said on Wednesday the reports were a \"premeditated provocation\" aimed at undermining the chances of all sides agreeing to sit down for peace negotiations first mooted by Moscow and Washington in May.