Paris: US Secretary of State John Kerry here on Sunday urged Syrian warring parities to respect cessation of hostilities, a day ahead of the resumption of the United Nations-brokered Syrian peace talks in Geneva. Kerry said some 600 combatants of the Islamic State (IS) have been killed during the past three weeks of US-led coalition strikes in Syria, stressing that the operation will be intensified, Xinhua reported. He made the remarks after a meeting on Syria with his counterparts from France, Germany, Italy and Britain in Paris on Sunday. "All parties must respect the cessation of hostilities, cooperate in the delivery of humanitarian aid, and respect the process of negotiations to achieve a political transition," said Kerry at a press conference with his European counterparts. French Foreign Minister Jean-Marc Ayrault said in order to "guarantee the credibility of the negotiations (in Geneva), the unimpeded humanitarian access and the truce in Syria must be fully respected". Ayrault also said the Geneva talks would be "difficult" but had to focus on "real political transition" in Syria. The foreign ministers of France, Germany, Italy and Britain, along with John Kerry also expressed their full support to the Libyan national unity government.