Either Syrian rebels or the Damascus regime have used chemical weapons in the country's two-year civil war, Israel's Intelligence Minister Youval Steinitz said on Wednesday.
"It's clear that chemical weapons have been used against civilians by the rebels or by the government," Steinitz told Israeli army radio.
"This is very concerning for us and we must deal with it urgently."
Syrian rebels and the regime exchanged accusations of chemical weapons use on Tuesday for the first time in the conflict that started as a peaceful uprising in March 2011.
Russia and Iran, both allies of President Bashar al-Assad, said they had received information proving rebels had used chemical agents in an attack in the northern province of Aleppo, which an official toll said killed 31 people.
The United States, which is among a number of Western and Arab countries supporting the Syrian opposition leadership, said the accusations were baseless, and warned the regime against using chemical weapons.
Israel's army, which patrols its northern border with Syria, said in a separate statement that four injured Syrians were treated by its soldiers.
"Early this morning four wounded Syrians came to the Israel-Syria border and received medical treatment from soldiers. Two... were taken to Israeli hospitals," it said.