British Government: It's "Highly Likely" Assad Regime Was Behind Use of Chemical Weapons Last Week

Military has made plans for intervention

(CNN) -- It's "highly likely" that the Syrian government is behind the use of chemical weapons that killed hundreds last week on the outskirts of Damascus, the British government said Thursday in a public version of its intelligence assessment into the attacks.

"It is not possible for the opposition to have carried out a (chemical weapons) attack on this scale," the British Joint Intelligence Organisation said in the assessment. The agency said it was confident as well that Syrian authorities had used chemical weapons at least 14 times before.

Western powers are debating using military power to counter the August 21 attack, which was much larger and deadlier than earlier assaults, saying it violates international norms.