The White House on Wednesday said it is concerned that international inspectors have received "credible allegations" that chemical weapons are still being used in Syria, Reuters reports.
Diplomats said last week that international inspectors had found traces of sarin and VX nerve agent at a military research site in Syria that had not been declared to the global chemical weapons watchdog, the Organization for the Prohibition and Chemical Weapons (OPCW), despite Syria’s pledge to do so.
"We're aware that the OPCW continues to receive credible allegations that the use of chemical weapons in Syria is still taking place," White House spokesman Josh Earnest was quoted as having told reporters in a briefing.
"Attempts by the OPCW to resolve some gaps and inconsistencies in Syria's declaration of their chemical weapons have gone unresolved," he added.
In 2013, the United States threatened military intervention against Syria's government after sarin gas attacks that year killed hundreds of residents in Ghouta, a rebel-controlled suburb of the Syrian capital Damascus.
The Damascus government forestalled foreign intervention by agreeing to a U.S.- and Russian-brokered deal under which it joined the OPCW, admitting to having a chemicals weapons program and promising to eliminate it.
A joint mission between the UN and the OPCW was then tasked with eliminating Syria's chemical weapons program, and the government of President Bashar Al-Assad last year handed over 1,300 tons of chemical arms.
Damascus has denied using sarin or any chemical weapons in battle during Syria's continuing civil war.
The finding of VX and sarin supports assertions by Western governments that Assad withheld some of his stockpile, or did not disclose the full extent of Syria's chemical capability or arsenal to the OPCW.