US Secretary of State John Kerry said on Monday he hoped the Crimea crisis would not harm cooperation with Russia on international efforts to destroy Syria's chemical weapons.

"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 was due to attend a summit of the G7 leading industrialized nations.

"This is bigger than either of our countries. This is a global challenge," Kerry said.

"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, which won the Nobel Peace prize last year, and was also due to meet the OPCW's Turkish head, Ahmet Uzumcu.

- Reuters