Members of the UN Security Council called Wednesday for an investigation into new claims of a chlorine gas attack on a rebel bastion in Syria, expressing concern over the reports.

The 15-member organization was briefed behind closed doors by Sigrid Kaag, who coordinates a mission in Syria to oversee the removal of its chemical weapons stockpile by June 30.

Members "expressed concern about alleged reports about the use of chlorine gas in some towns, which left people dead and injured, and called for an investigation of this incident," said the ambassador of Nigeria, which holds the rotating presidency.

When pressed by reporters, Nigerian ambassador Joy Ogwu gave no further details on who or how such an inquiry might be conducted.

"We're still waiting to confirm the authenticity of the reports. Until we have the full facts we cannot take any decision on this matter," Ogwu said.

She said there was "no decision" on who should investigate. "We heard a briefing and we made comments on the briefing," she said.

France and the United States allege that Assad's forces may have unleashed industrial chemicals on a rebel-held village in central Hama province this month.

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.

Syrian ambassador Bashar Jaafari categorically denied that government forces were using chlorine gas.

"The aim of this kind of allegations emanating from Washington or elsewhere is to overshadow the successful preparations for the presidential elections in Syria," he said.

Damascus has announced plans to hold a presidential election on June 3, despite the three-year war raging across the country.

On Tuesday, the Organisation for the Prohibition of Chemical Weapons said Syria has handed over 86.5 percent of its arsenal.

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.