Israeli Prime Minister Benjamin Netanyahu on Thursday called the possible use of chemical weapons in Syria "terribly disturbing", accusing Iran of using the country as a "testing ground".
"The reported use of chemical weapons against innocent civilians is terribly disturbing," he said in a statement.
Syria's main opposition group on Wednesday accused the government of "massacring" more than 1,300 people in chemical weapons attacks near Damascus, saying many of the victims choked to death, a claim later supported by Israeli Defence Minister Moshe Yaalon.
"If verified, it will be a horrible addition to the roster of tragic crimes committed by the Syrian regime against its people," Netanyahu said.
The reports of the chemical attack came as a team of UN inspectors was in Syria to probe previous allegations of chemical weapons strikes levelled against both sides during the 29-month conflict.
Netanyahu said the fact the regime prevented the UN investigators from reaching the area was "absurd", warning the world's inaction on Syria could encourage Iran to push ahead with its nuclear programme.
"Syria has become Iran's testing ground," he said. "Iran is closely watching how the world responds to the atrocities committed by its client state Syria and its proxy Hezbollah.
"These events prove yet again that we simply cannot allow the world's most dangerous regimes to acquire the world's most dangerous weapons," Netanyahu said.
Earlier this month, Netanyahu urged "increased pressure" on Iran, saying it was the "only thing" that would deter it from pursuing nuclear weapons capability.
Israel and other Western countries suspect the Islamic republic is using its nuclear programme -- which Tehran insists is for peaceful purposes -- to develop an atomic bomb.