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Israel has voiced doubt about the accuracy of Syrian activists' reports that chemical weapons had been used against rebels fighting to topple President Bashar al-Assad.
"We have seen reports from the opposition. It is not the first time. The opposition has an interest in drawing in international military intervention," Vice Prime Minister Moshe Yaalon said on Army Radio.
"As things stand now, we do not have any confirmation or proof that (chemical weapons) have already been used, but we are definitely following events with concern," he said.
The Syrian Observatory for Human Rights gathered activist accounts on Sunday (local time) of what they said was a poison gas attack in the city of Homs. The reports are difficult to verify, as the government restricts media access in Syria.
The Observatory, a British-based group with a network of activists across Syria, said those accounts spoke of six rebel fighters who died after inhaling smoke on the front line of Homs's urban battleground. It said it could not confirm that poison gas had been used and called for an investigation.
Syria has said it would never use chemical weapons against its citizens.
Asked about images purported to show patients being treated for possible gas poisoning, Yaalon said: "I'm not sure that what we're seeing in the photos is the result of the use of chemical weapons.
"It could be other things," he said, without elaborating.
On Sunday, senior Israeli defence official Amos Gilad said Syria's chemical weapons were still secure despite the fact that Assad had lost control of parts of the country.
As Syria's southern neighbour, Israel has been concerned about chemical weapons falling into the hands of Islamist militants or Lebanese Hezbollah fighters, cautioning it could intervene to stop such developments.