The United States says chemical attacks were likely launched in Syria this month, possibly by the regime, weeks before an announced presidential election set for June 3.
"We have indications of the use of a toxic industrial chemical, probably chlorine, in Syria this month, in the opposition-dominated village of Kafr Zita," White House spokesman Jay Carney said.
"We are examining allegations that the government was responsible."
The revelation follows Sunday's announcement by French President Francois Hollande that his country had "information" but no proof that Syrian President Bashar al-Assad's regime was still using chemical weapons.
There are conflicting accounts about one attack that happened in Kafr Zita in the central Hama province in April, with both the government and the opposition accusing each other.
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The State Department also pointed to indications of a chemical attack.
"Obviously there needs to be an investigation of what's happened here. We're working with our partners to determine what the facts are on the ground," State Department spokeswoman Jen Psaki said.
The fresh accusations come as the Organisation for the Prohibition of Chemical Weapons and other experts work to remove the Assad regime's chemical stockpiles, following an agreement reached after deadly chemical attacks outside Damascus last August that the West blamed on Assad's regime.
The OPCW said last week that 65 per cent of Syria's stated chemical weapons have been removed from the country.
The most dangerous are being transferred to a US Navy vessel specially fitted with equipment to destroy the chemicals at sea.
Meanwhile, Assad announced Monday that Syria will hold a June 3 presidential election despite a brutal civil war that has killed 150,000 people since March 2011.
The move is expected to return Assad to power but Washington slammed it as "a parody of democracy."
"He is making a mockery of his own pretensions to being a democratically elected leader," Carney said.
"A presidential referendum, which is what this would be, is a parody of democracy and would have no credibility or legitimacy within Syria or outside of Syria."
Psaki said the elections would ring especially hollow in the midst of such devastation.
"Staging elections under current conditions, including the effective disenfranchisement of millions of Syrians, neither addresses the aspirations of the Syrian people nor moves the country any closer to a negotiated political solution," she told reporters.
