The chemical weapons allegedly used to kill hundreds of Syrian civilians by the regime of President Bashar Assad last Wednesday were fired by the 155th Brigade of the 4th Armored Division of the Syrian Army, an Israel TV report said.

This division is under the command of the president’s brother, Maher Assad.

The nerve gas shells were fired from a military base in a mountain range to the west of Damascus, the Channel 2 news report said.

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The embattled regime has concentrated its vast stocks of chemical weaponry in just two or three locations, the report said, under the control of Syrian Air Force Intelligence, itself reporting to the president.

The TV report further added that “the assessment in Israel” is that the attack was intended to serve as the possible start of a wider operation.

It said Israel was increasingly concerned about the use of chemical weapons in Syria, and their possibility of these weapons falling into still more dangerous hands than those of Assad. Israel was “privately” making clear its concerns to the United States, the report said.

In his first response Thursday to the alleged attack, Israel’s Prime Minister Benjamin Netanyahu warned that Iran was closely watching how the world would deal with the attack.

“Syria has become Iran’s testing ground, and Iran is closely watching whether and how the world responds to the atrocities committed there by its client state Syria and its proxy Hezbollah against innocent civilians in Syria,” he said.

The alleged use of chemical weapons against Syrian civilians on Wednesday “proves yet again that we cannot permit the world’s most dangerous regimes to acquire the world’s most dangerous weapons,” Netanyahu added.

On Wednesday, rebel groups in Syria claimed that as many as 1,300 people were killed in a chemical attack in the eastern suburbs of the capital Damascus. The reports were accompanied by a string of grisly photos and videos depicting scores of dead civilians, including children.

The reports “raise the possibility that an extremely grievous crime has been committed by the Syrian regime against its citizens,” Netanyahu said.

“This act adds to the roster of crimes committed by the Syrian regime, with the aid of Iran and Hezbollah, against the Syrian people,” he said.

Netanyahu added that it was “absurd that UN investigators, who are in Damascus right now to investigate the possibility that chemical weapons have been used, are being prevented by the Syrian regime from reaching the affected areas.”