On Saturday, activists said the Syrian government used chlorine gas while bombing Douma, the last rebel-held area in the Eastern Ghouta countryside of Damascus.
"The seriousness of the recent allegations requires a thorough investigation using impartial, independent and professional expertise", he said.
He said the United States is trying to get an inspection team from the Organization for the Prohibition of Chemical Weapons to the site of the alleged attack.
The U.N. Security Council is preparing to meet in an emergency session Monday to discuss a suspected chemical attack in Syria, as Russia's chief diplomat said there was no evidence one ever happened. Russian Federation voted for the cease-fire but has repeatedly used its veto power as a permanent member to block any measure that threatens a Syrian offensive against rebels, largely to protect its ally, the government of Syrian President Bashar al-Assad.
Washington and Moscow set out starkly different positions at a stormy emergency session at the UN Security Council, where Russia's ambassador Vassily Nebenzia warned that the possibility of USA military action was "very, very risky".
The Security Council meeting is shaping up to be a rematch of previous debates on civilian casualties in Syria. He said the United States is considering a response, including military attacks.
"This attack that took place in Douma is a barbaric attack".
A White House statement released later said the United States is continuing to assess intelligence and is engaged in conversations with its partners and allies.
The Syrian Foreign Ministry said Tuesday that it has sent United Nations an invitation for a fact-finding mission to investigate the allegations of chemical weapons use in Damascus' eastern district of Douma, state news agency SANA reported.
Lavrov said Russian Federation would propose a "transparent and honest" investigation with the involvement of the Organisation for the Prohibition of Chemical Weapons at the Security Council on Tuesday.
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