The British government has "limited but persuasive information" that chemical weapons - including sarin - have been used in Syria, dpa cited Downing Street as saying Thursday. "Use of chemical weapons is a war crime. We have briefed our allies, partners and the UN on this information and we are working actively to get more and better information," a government spokesman said. The development was "extremely concerning," he said, and called on Syrian al-Assad's regime to allow unrestricted access to international inspectors.