"There are strong indications there was a chemical weapons attack - clearly by the government," the official said, following reports that a chemical attack had left anywhere from 500 to well over 1,000 people dead in the rebel-held suburbs of Damascus.
U.S. President Barack Obama has said in the past that if proof was found that the Syrian military used chemical weapons, it would be a "game changer" for American involvement in the civil war there. Obama has also described the deployment of chemical or biological weapons in Syria as a "red line."
The Syrian government has vehemently denied the accusations, accusing rebel forces of fabricating the claims or staging gas attacks themselves, according to the Wall Street Journal. "These claims are categorically false and completely baseless and are part of the filthy media war waged by some countries against Syria," a spokesman for Syria's armed forces reportedly said.
Meanwhile, UN Secretary-General Ban Ki-moon asked the Syrian government on Thursday to allow UN inspectors to investigate the allegations "without delay" and grant them access to the site in the Damascus suburbs.
Ban has asked UN High Representative for Disarmament Affairs, Angela Kane, to travel to Damascus to push for access for the UN team, which arrived in Syria on Sunday to investigate several previous claims of chemical weapons use.
"The Secretary-General believes that the incidents reported yesterday need to be investigated without delay," Ban's press office said in a statement. "A formal request is being sent by the United Nations to the government of Syria in this regard. He expects to receive a positive response without delay."
Israel also on Thursday responded to the alleged attack, saying it believed Syrian forces had used chemical weapons, and accused the world of turning a blind eye to such attacks.
Prime Minister Benjamin Netanyahu said if Syria is not punished, its ally Iran could be encouraged to develop nuclear weapons.
"Syria has become Iran's testing ground, and Iran is closely watching whether and how the world responds to the atrocities committed by Iran's client state Syria ... against innocent civilians in Syria," Netanyahu said in a statement.
"These events prove yet again that we simply cannot allow the world's most dangerous regimes to acquire the world's most dangerous weapons."
Opposition activists have accused Assad's forces of gassing hundreds, including women and children, on Wednesday, allegations which government officials deny.
French Foreign Minister Laurent Fabius said on Thursday the international community needed to respond with force if the allegations of a Syrian government chemical attack proved true, although there was no question of sending troops on the ground.
For Israel, the conflict in its northern neighbor is a battle between two evils: Assad - who is allied with two of its most strident enemies, Iran and Lebanon's Hezbollah guerrillas - and Sunni jihadists fighting with rebels to oust him.
Wednesday's incident, carried out while UN inspectors were in Damascus to look into allegations of earlier chemical attacks by Syrian President Bashar Assad's forces, was seized by Israel as an opportunity to question international resolve to curb its foes' suspected pursuit of weapons of mass destruction.
"It is absurd that the UN investigators, who are right now in Damascus to verify use of chemical weapons, are prevented from reaching the afflicted areas by the Syrian regime," Netanyahu said.
The Assad government has denied using chemical weapons against Syrians. Iran denies seeking nuclear weapons. Israel is widely assumed to have the Middle East's only nuclear arsenal.
Interviewed on Israel Radio, Strategic Affairs Minister Yuval Steinitz said that according to "Israeli intelligence assessments," chemical weapons had been used in the rebel-held eastern Damascus suburbs, and "not for the first time" in Syria's civil war.
"Nothing tangible or significant has been done in the past two years to halt Assad's incessant massacre of his citizens," Steinitz said. "The world condemns, the world investigates, the world pays lip service."
Israel has stopped short of urging Western military intervention in the Syrian conflict.
Israel has on several occasions taken action of its own, firing into Syria after mortar bombs and shells from battles near the frontier struck inside the Golan Heights, which it captured from Syria in a 1967 war.
Transportation Minister Yisrael Katz said the alleged horror of gas attacks on Syrians resonated strongly in the Jewish state, founded after the Nazi Holocaust in which many of the six million Jewish dead were killed in gas chambers.
Israel has long conducted a national gas mask distribution program for the civilian population. It has accused Syria of stockpiling chemical weapons and voiced concern they could be transferred to Hezbollah or other hostile groups.
"Today he (Assad) is murdering his own people, tomorrow he will threaten us and perhaps worse," Katz told Israel Radio.
The UN team, led by Swedish scientist Ake Sellstrom, is currently looking into three claims of chemical weapons use in the Syrian conflict.
The United Nations has received a total of 14 reports of possible chemical attacks - one from Syria's government and the rest from Britain, France and the United States.
The Syrian government and the opposition have accused each other of using chemical weapons, and both have denied it. The UN inquiry will try to establish only whether chemical weapons were used, not who used them.
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