Britain's U.N. envoy said on Tuesday reports of a chemical weapon attack in Syria had not yet been "fully verified" as the Russian Foreign Ministry accused Syrian rebels of using chemical weapons near the northern city of Aleppo.
Syria's government and rebels accused each other of launching the deadly chemical attack on Tuesday. If confirmed it would be the first use of such weapons in the two-year-old conflict.
"We have seen those reports, they haven't yet been fully verified," Britain's U.N. Ambassador Mark Lyall Grant told reporters on his way into a U.N. Security Council meeting on Afghanistan.
"But clearly if chemical weapons were used then that would be abhorrent and it would require a serious response from the international community," he said.
U.N. spokesman Martin Nesirky told reporters: "We're aware of the reports but we're not in a position to confirm them."
Nesirky added that if either side used chemical weapons it would be a "grave violation of international law" and an "outrageous escalation" of the Syrian conflict.
The Security Council has been deadlocked on Syria since 2011. Russia and China have refused to consider sanctions on President Bashar al-Assad's government and have vetoed three resolutions condemning Assad's crackdown on opposition groups.
In Moscow, the Russian Foreign Ministry said in a statement:
"According to information coming from Damascus, a case of the use of chemical weapons by the armed opposition was recorded early in the morning of March 19 in Aleppo province."
The conflict began as peaceful protests that turned violent when Assad tried to crush the revolt. The United Nations says more than 70,000 people have been killed and more than 1 million people have fled the violence.
Australian Foreign Minister Bob Carr called for the Security Council to take action if reports of a chemical weapon attack were verified. He described the reports as "deeply alarming."
"We unreservedly condemn it. We will move with others of course if these reports are verified to bring it before the Security Council," Carr told reporters at the United Nations, after he spoke to the council meeting on Afghanistan.