TEL AVIV, March 20 (RIA Novosti) - US President Barack Obama said Wednesday he was “deeply skeptical” of Syrian government claims that its opponents used chemical weapons in the civil conflict there, but warned any use of such arms would be a fundamental “game changer” in the world’s action on the crisis.

“I am deeply skeptical of any claim that in fact it was the opposition that used chemical weapons,” Obama told journalists in Jerusalem at a joint news conference with Israeli Prime Minister Benjamin Netanyahu.

“Anyone who knows the facts of the chemical weapons stockpiles inside of Syria, as well as the Syrian government capabilities, I think would question those claims,” Obama said.

His comments came a day after the Syrian government and opposition rebels each accused the other of having used chemical arms during fighting in the northern Syrian city of Aleppo.

Shortly before Obama spoke, the US ambassador to Syria, Robert Ford, told a congressional panel that “so far we have no evidence to substantiate those reports” on use of chemical weapons.

However, a senior Israeli official, Yuval Steinitz, the newly appointed minister of intelligence and strategic affairs, told Israeli Army Radio that it was “apparently clear” that chemical weapons were used recently in Syria, according to the Associated Press.

He did not say which side allegedly used the weapons. But in its report from Jerusalem, the AP cited another unnamed Israeli official as concurring with the assessment that chemical weapons were used.

And in a statement on Tuesday, the Russian Foreign Ministry appeared to accept as fact the reported use of chemical weapons in Aleppo, describing this as an “extremely dangerous” development in the Syrian conflict.

The United States has described the government under Syrian President Bashar al Assad as “discredited” and has thrown its political support behind rebels fighting to topple him, but stopping short of providing military assistance to them.

Russia by contrast has consistently warned against outside intervention aimed at “regime change” in Syria, insisting that its support is not for the Assad regime but for international law and urging caution in dealing with rebel groups whose composition and aims are uncertain.