(GENEVA) -- The U.N.'s special envoy to Syria announced Wednesday that evidence suggests a "chemical substance" was used to kill hundreds of people in Syria last week, but the U.N. pleaded for more time before the U.S. and allies launch a retaliatory strike against the Syrian regime.
The announcement comes as the U.S., France and Britain gear up for a military strike on the Syrian regime.
Speaking to reporters in Geneva, special envoy Lakhdar Brahimi said, "With what has happened on the 21st of August last week, it does seem that some kind of substance was used that killed a lot of people: hundreds, definitely more than a hundred, some people say 300, some people say 600, maybe 1,000, maybe more than 1,000 people."
But Brahimi did not place the blame on the regime or the opposition. He also added, "International law says that any U.S.-led military action must be taken after" agreement in the U.N. Security Council.
U.N. Secretary-General Ban Ki-moon has asked for another couple of days, saying "the team needs time to do its job" on the ground.
The U.N. chemical weapons inspection team in Syria came to the conclusion after spending just a day and a half at the sites of last Wednesday's attack in a suburb of the capital of Damascus.
Video uploaded Wednesday by local activists shows the U.N. convoy entering Mleha, in the Damascus suburb of eastern Ghouta, the U.N. team's first visit to the main attack site. The U.N. convoy came under fire on Monday and the team postponed their field visit Tuesday due to security concerns.
U.N. Secretary-General Ban Ki-moon has asked for an extension, saying "the team needs time to do its job" on the ground.
Speaking in The Hague on Wednesday, Ban joined Brahimi to urge the international community to work within the U.N. framework.
"The body entrusted with international peace and security cannot be missing in action," he said. "The Council must find the unity to act. It must use its authority for peace."
Later, Britain will introduce a resolution to the U.N. Security Council "authorizing necessary measures to protect civilians" in Syria. According to a Downing Street spokesman, the U.K. will call for authorization of all measures under Chapter 7 of the U.N. Charter, which could include breaking diplomatic ties and economic sanctions, or action by air, sea or land forces.
British Prime Minister David Cameron tweeted Wednesday morning, "we've always said we want the UN Security Council to live up to its responsibilities on Syria. Today they have an opportunity to do that."
Russia, a staunch supporter of Syrian President Bashar Al-Assad, and China will veto any Security Council resolution that includes military action. But the Obama administration may not wait for U.N. approval.
Asked if the U.S. was ready to act just "like that," U.S. defense secretary Chuck Hagel said: "We are ready to go, like that."
In the last 24 hours, Washington has ramped up its case against the Syrian regime.
White House spokesman Jay Carney said Tuesday that allowing "the use of chemical weapons on a significant scale to take place without a response would present a significant challenge to, threat to the United States' national security."
As the rhetoric strengthens, the administration has yet to distribute a promised intelligence report pinning the attack squarely on the Syrian regime.
On Tuesday, Syria's Foreign Minister challenged the Obama administration to show proof linking Assad to the attack.
"If they have any evidence of our use [of chemical weapons], I challenge them to show this evidence to [global] public opinion," he said at a press conference in Damascus. "It's the right of public opinion to know the truth of these allegations."
A Syrian army source told the Iranian news agency FARS, "If Damascus comes under attack, Tel Aviv will be targeted too."
The source added, "We are rest assured that if Syria is attacked, Israel will also be set on fire."
Iran's Supreme Leader Ayatollah Ali Khamenei also voiced his opposition to a U.S. military strike today, calling it a "disaster."
"The intervention of America will be a disaster for the region," Khamenei said, according to the Iranian state news agency ISNA. "The region is like a gunpowder store and the future cannot be predicted."
Israel's cabinet has called up a limited enlistment of reserve forces and Israeli Army Radio reports Israel has reinforced its missile defenses as a precaution against possible retaliatory attacks. Israel's defensive arsenal includes the short-range Iron Dome missile interceptors, the mid-range Patriot and the long-range Arrow II.
Israeli Prime Minister Netanyahu told his nation "there is no reason to change daily routines," and echoed his statement from Tuesday saying "we are prepared for any scenario."
Israeli media reports a run on gas masks and local TV stations showed video of long lines at a free gas mask distribution center in Tel Aviv.
But Israelis aren't worried yet, according to Col. Yechiel Kuperstein, the former head of the Home Front Command's Physical Protection Department.
"Israelis can't panic," Kuperstein told told ABC News. "We know how to do it, but not at the moment. I think it is too far away. The threat is too far away for the people to be in panic."
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