THE HAGUE - US Secretary of State John Kerry said on Monday he hoped the Crimea situation would not impact cooperation with Russia on international efforts to destroy Syria's chemical weapons."I hope not. All I can say is I hope the same motivations that drove Russia to be a partner in this effort will still exist," Kerry told reporters in the Hague, where he is planning to attend a G7 summit.Syrian President Bashar Assad's government agreed to destroy its chemical weapons arsenal after a chemical attack killed hundreds of people around Damascus last year. "This is bigger than either of our countries. This is a global challenge," Kerry said.Syria has missed almost all deadlines agreed in the deal brokered by Kerry and his Russian counterpart Sergei Lavrov, whom he is due to meet for bilateral talks in The Hague. Syria is several weeks behind schedule in handing over its toxic stockpile.Plans for a joint mission between Russia and NATO to protect a US cargo ship that will destroy Syria's deadliest chemical weapons have been cancelled amid increased tensions over Russia's annexation of the Crimea.Kerry, who made no further allusion to Crimea in his remarks, noted that the Syrians had also missed a March 15 date for destruction of a dozen production and storage facilities."We have some real challenges ahead of us in these next weeks. We in the United States are convinced that if Syria wanted to they could move faster," he added. Kerry confirmed that about half of Syria's declared chemical weapons arsenal has been shipped out or destroyed within the country."We are just about at the 50 percent removal mark. That is significant but the real significance would only be when we get all the weapons out," he said.Kerry was speaking at the Organisation for the Prohibition of Chemical Weapons (OPCW), which won the Nobel Peace prize last year, and was also due to meet the OPCW's Turkish head, Ahmet Uzumcu. Iranian talksLast week Moscow said it would respond in kind to US sanctions imposed on Russian officials over the Crimea dispute and is considering other steps if Washington escalates tensions, Deputy Foreign Minister Sergei Ryabkov said on Wednesday.The United States and the EU announced last Monday sanctions on a handful of officials from Russia and Ukraine accused of involvement in Moscow's seizure of Ukraine's Crimea region, most of whose 2 million residents are ethnic Russians. Moscow will respond in kind to US sanctions imposed on Russian officials over the Crimea dispute and is considering other steps if Washington escalates tensions, Deputy Foreign Minister Sergei Ryabkov said after the sanctions were imposed. Ryabkov gave few details on what form those measures could take but suggested that six-party talks over Iran's nuclear program could provide a means of response."Moscow would not want to use these talks as an element of raising the diplomatic stakes," he said."But if we are forced, we will follow here a path of responsive measures because in the end the historical importance of what has happened in the last days and weeks regarding the ... reunification of Crimea with Russia is incomparable to what we are doing regarding Iran."