Rebels, meanwhile, accused government forces of a chemical weapons attack on the rural Damascus suburb of Ateibeh.
Last week, Syrian rebel spokesman Louay al Mokdad claimed opposition fighters had captured an unexploded canister from an alleged chemical weapons attack.
Kurds in northern Iraq have been commemorating the 25th anniversary of the chemical weapons attack on the town of Halabja by Saddam Hussein's forces.
This week the French announced the arrest of what appears to be an al-Qaida cell whose members were planning a chemical weapons attack on the Paris subway.
Not long ago, the Bush administration quietly asserted that it might use nuclear weapons in a conflict first if the US suffers a biological or chemical weapons attack.
Anthony Loyd, a journalist for the Times newspaper, told the BBC about the aftermath of one suspected chemical weapons attack earlier this month in the northern city of Aleppo.
BBC: 'Growing evidence' of chemical weapons use in Syria - UK
While Ban told reporters at the United Nations he was aware of the rebel claims of a chemical weapons attack by the government, he did not say whether those claims will also be investigated.
An analysis of video of hospitalized Syrians released by state-run TV suggests people are not suffering from a chemical weapons attack, nor are they being treated as though they were in such an attack, the U.S. military official said.
U.S. or its allies suffering one chemical or biological weapons attack or many.
CENTERFORSECURITYPOLICY: ��De-alerting�� Nukes Would Imperil U.S. Security
Syria claimed rebels used chemical weapons in an attack Tuesday in Khan al-Asal in the northern province of Aleppo.
They've sent a very clear message to our enemies that a chemical or a biological weapons attack on this nation could be met with and likely would be met with a nuclear response.
Asked what they though terrorists might do next, 37 percent said attack with chemical or biological weapons, while 18 percent expect a bombing or an attack on a public place or infrastructure.
With or without chemical arms control agreements, the United States will continue to confront adversaries equipped with CW. If it wishes to minimize the chances that it will be the victim of chemical attacks, the U.S. must retain a modest, but reliable, capability to respond to any such attack with chemical weapons.
The Syrian government called for the United Nations to investigate alleged chemical weapons use by rebels in the attack that killed 31 people.
He has used chemical weapons against the Kurdish people in an attack on a genocidal scale, and he has sent his forces into Kurdistan to conduct widespread slaughter.
It is Fatah that is threatening to renew shooting attacks on Jerusalem and attack Israel with chemical and biological weapons.
CENTERFORSECURITYPOLICY: Olmert��s response to Palestinian violence
The Assad regime spent years buying up sophisticated long range missiles, air defense systems and chemical weapons to counter the threat of an airborne attack from Israel.
"There is regrettably little that the United States can do to ensure the safety of its servicemen and women now exposed to imminent threat of attack by Iraqi chemical and other weapons of mass destruction acquired with the help of German firms, " said Frank J.
He's now told the world we'll never again use our nuclear weapons as a deterrent against a chemical or a biological attack.
Charges that Assad's forces used chemical weapons surfaced months ago, but it was a March 19 attack in Aleppo that drew global attention.
In a separate development, UN Secretary General Ban Ki-moon said he was waiting for the Syrian government to allow a team of chemical weapons experts into the country for an expanded investigation following an attack on a village outside Aleppo in March.
BBC: Syria crisis: Bashar al-Assad says West will 'pay price'
Damascus says rebel forces used chemical weapons, but rebel commanders have accused government forces of carrying out the attack, citing reports of victims suffering breathing difficulties and bluish skin.
The document will say "there remains a narrow range of contingencies in which the option of using nuclear weapons can play a role in deterring large-scale conventional, chemical or biological attack, " he said.
Before the attack in Aleppo on Tuesday, Syria's government had never alleged rebels had access to chemical weapons, only refuting rebel claims last year that it had used such weapons or ever would against its own people.
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