Israel’s Channel 10 said the officials feared that the outfit calling itself Yarmouk Martyrs Brigade may be planning to test the weapons.
“The group was not currently concerned with Israel and was not directing offensive efforts against it, being preoccupied with fighting other groups in the Syrian civil war,” the television said.
“Any chemical weaponry in their hands was thus not considered an immediate threat to Israelis,” it added.
ISIS reportedly carried out a chemical attack on a Syrian military airport in Deir Ezzor earlier this month.
In March, local Iraqi governor Najmuddin Kareem also told Reuters that the group had used “poisonous substances” during an attack on the village of Taza in northern Iraq.
Channel 10 said the ISIS affiliate, based in the Golan Heights not under the Israeli occupation, had obtained the weapons "recently."
Damascus surrendered its stockpiles of chemical weapons to a joint mission led by the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) following an attack outside the Syrian capital two years ago.
The August 21, 2013 attack saw chemical weapons being used in the Ghouta suburb of Damascus in which hundreds of people died in the attack. According to reports, the rockets used in the assault were handmade and contained sarin.
Last December, Ahmed al-Gaddafi al-Qahsi, a cousin of former Libyan dictator Muammar Gaddafi, alleged that the chemical weapons used in Ghouta were stolen from Libya and later smuggled into Syria via Turkey.
Israel is widely known to have treated militants fighting to topple Syrian President Bashar al-Assad.
According to Israel's Channel 2 television, the number of militants having received treatment since 2011 has reached 2,100.
In December 2015, the British newspaper Daily Mail said the Israeli regime had saved the lives of more than 2,000 Takfiri militants since 2013.
The Syrian army has repeatedly seized sizable quantities of Israeli-made weapons and advanced military equipment from militants in Syria.
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