Syria has handed over 86.5 percent of its chemical weapons, the global chemical watchdog said on Tuesday, amid new claims that Damascus may have launched attacks with an industrial chemical earlier this month.

The latest update comes five days before a self-imposed cut-off of April 27, by which Damascus aimed to have its stockpile removed from Syrian soil, ahead of a June 30 deadline to destroy it.

A further consignment of chemicals was delivered to the main Syrian port of Latakia on Tuesday, raising "the overall portion of chemicals removed from Syria to 86.5 percent of the total", the Organisation for the Prohibition of Chemical Weapons (OPCW) said in a statement.

"Today's consignment was the 17th to date and the sixth consignment since April 4, making a significant acceleration in the pace of deliveries to Latakia this month," the Hague-based OPCW added.

Upon arrival, the chemicals were "immediately" put onto cargo ships and "removed from the country".

"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."

Under the terms of a US-Russia brokered deal reached last year, Syria has until the end of June to destroy its chemical weapons if it wants to ward off the threat of US air strikes.

The agreement was reached after deadly chemical attacks outside Damascus last August which the West blamed on President Bashar al-Assad's regime.

However, new claims have emerged that the regime may have launched attacks with chlorine gas this month, including in an opposition-held part of the country.

Both government and rebels are trading blame for an attack in opposition-held Kafr Zita in the central province of Hama earlier this month.

Activists have also reported other chlorine gas attacks, most recently on Monday in the northwestern province of Idlib.

The latest claims, cited by the United States and France, come as Syria plans to hold a June 3 presidential election, which the United Nations and the Syrian opposition have condemned as flying in the face of efforts to end the country's three-year war.