Syrians in the rebel city of Homs endured an eleventh straight day of violent attacks by the country's military.
Activists called Tuesday's events some of the heaviest shelling since the siege began. Hundreds in Homs have died and residents may soon run out of water.
A defecting officer from the Syrian army said President Bashar Assad used nerve gas to speed the invasion of Homs. He claims Russian and Iranian scientists aided the army.
Troops loyal to Assad have been shelling Homs for more than a week in an effort to retake parts of the city captured by rebels.
The Arab League said it may soon arm the Syrian opposition if Assad doesn't stop the attack.
A count by the United Nations last month revealed that the uprising violence has killed more than 5,400 people.