The world's chemical weapons watchdog said today that allegations a chemical attack took place in the Syrian rebel-held town of Khan Sheikhun, killing at least 87 people, were "credible".<br/>'<br/>Following last week's deadly attack, the Organisation for the Prohibition of Chemical Weapons said technical experts analysed the available information "and their preliminary assessment was that this was a credible allegation".<br/>'<br/>Ahmet Uzumcu, the OPCW's director general, told members of the 41-state executive council that a fact-finding mission had already collected samples after the attack, which were sent to OPCW designated laboratories for analysis.<br/>'<br/>Uzumcu said in a statement, released from its Hague-based headquarters, that OPCW experts are currently analysing all information gathered from various sources" and is expected to complete their work within the next two to three weeks. <br/><br/>He also reiterated his call for any countries that were signatories to the Chemical Weapons Convention and which were in a position to do so to share with the Secretariat any relevant information without delay.<br/>'<br/>The watchdog's executive council will meet again next week to continue the discussions over the April 4 attack at Khan Sheikun, Uzumcu said. <br/><br/>Russia yesterday vetoed a UN resolution demanding the Syrian government cooperate with an investigation into the alleged chemical attack, blocking Security Council action against its ally for an eighth time.