The chemical weapons watchdog said Tuesday that Syria has handed over 86.5 percent of its arsenal as new claims emerged of an attack on a rebel bastion this month using an industrial chemical.
Under the terms of a US- and Russian-brokered deal which averted the threat of US military action last year, Syria faces a June 30 deadline to destroy its chemical stockpiles.
The agreement was reached after deadly chemical attacks outside Damascus last August that reportedly killed hundreds. The West blamed President Bashar al-Assad's regime but the government said rebels were behind it.
The latest reports come as Syria, announced plans to hold a presidential election on June 3, despite the three-year war raging across the country.
The United Nations and the Arab League have warned that the vote, expected to return Assad to power, would be a blow to efforts for a negotiated peace.
The Organisation for the Prohibition of Chemical Weapons (OPCW) said a new consignment of chemicals was delivered Tuesday to the Syrian port of Latakia.
It raised "the overall portion of chemicals removed from Syria to 86.5 percent of the total", the Hague-based OPCW said in a statement.
The chemicals were immediately removed from the country in the 17th shipment since the operation began in October.
"This latest consignment (is) encouraging," said OPCW director general Ahmet Uzumcu.
"We hope that the remaining two or three consignments are delivered quickly to permit destruction operations to get under way in time to meet the mid-year deadline for destroying Syria's chemical weapons."
But his words were overshadowed by allegations from France and the United States that Assad's forces may have unleashed industrial chemicals on a rebel-held village in central Hama province this month.
France made the first claim Sunday with President Francois Hollande saying his country had "information" -- no proof -- that Assad's regime was still using chemical weapons despite the August deal.
On Monday the United States said it was investigating the allegations.
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"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," said White House spokesman Jay Carney.
- Prohibited weapon -
There have been conflicting accounts of the alleged chlorine attack on Kafr Zita, with the government and the opposition trading blame.
Activists have also reported other chlorine gas attacks, most recently in Idlib province, in the northwest, on Monday.
Chemical weapons expert Hamish de Bretton-Gordon said Syria was not required to declare its stockpile of chlorine -- a toxic but weak agent -- as it is widely used for commercial and domestic purposes.
"However, as a chemical weapon it is prohibited under the Chemical Weapons Convention," which Syria joined last year, said the expert, CEO of SecureBio, a British chemical weapons consultancy.
"The delivery method that we've seen -- the use of helicopters -- I am certain the opposition don't have any helicopters."
Syria announced on Monday that its first presidential election -- after constitutional amendments scrapped a referendum system -- will be held on June 3, with candidate registration closing on May 1.
"Such elections are incompatible with the letter and spirit of the Geneva communique," said UN spokesman Stephane Dujarric, referring to a 2012 agreement on a transition to democracy.
Arab League chief Nabil al-Arabi said that amid the "harsh human tragedy" of a war that has reportedly killed more than 150,000 people since March 2011, "it is not possible to organise transparent, democratic and credible presidential election".
The International Committee of the Red Cross said it was "appalled" by escalating violence in the main northern city of Aleppo, and called on the government to allow it access to deliver aid.