Syria still holds around eight percent of its chemical weapons material, missing a deadline to remove or destroy it all, the mission overseeing the destruction of its arsenal said Sunday.
Despite the slip, the head of the mission, Sigrid Kaag, said she was still hopeful a June 30 deadline for the complete destruction of the chemical arms would be met.
Parliament meanwhile announced that four new candidates had submitted applications to run in Syria's June 3 presidential elections.
On the ground, at least 21 people were killed when rebels carried out a mortar attack on regime-parts of the northern city of Aleppo, a monitoring group said.
Kaag told reporters in Damascus that 7.5-8.0 percent of Syria's declared chemical weapons material remained in-country, at "one particular site."
"However, 92.5 percent of chemical weapons material removed or destroyed is signficant progress," she said.
"We also however need to... ensure the remaining 7.5-8.0 percent of the chemical weapons material is also removed and destroyed."
Under a US-Russian deal negotiated last year, Syria signed up to the Chemical Weapons Convention and agreed to hand over its entire chemical arsenal by June 30 of this year.
Kaag acknowledged the security challenges facing the mission, but said Syria was required to meet its commitments nonetheless
"Success is around the corner and this last push is very much needed," she said.
"The 30 June deadline is around the corner... and we are hopeful that this is possible and will be met."
Meanwhile a lingering dispute remains over whether Syria will have to destroy 12 remaining chemical weapons production sites.
Damascus wants to seal the sites, which it says have already been rendered unusable, but Western countries want them completely destroyed, fearing that they may be reopened in the future.
There are also questions over alleged chlorine gas attacks in Syria in recent weeks, which the regime blames on a jihadist group but activists say were carried out by government forces.
Syria's government agreed to turn over its chemical arsenal last year as Washington threatened military action after a chemical weapons attack outside Damascus that reportedly killed some 1,400 people.
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Activists and much of the international community blamed the attack on the regime, which denied responsibility.
- New presidential candidates -
Parliament speaker Mohammad al-Lahham on Sunday said four more candidates would stand in the June 3 presidential election, bringing to six those competing against President Bashar al-Assad.
Assad, who has strongly suggested he will run, is widely expected to win the election although he has not yet announced his candidacy.
The four candidates announced Sunday are Sawsan Haddad, Samir Maala, Mohammed Firas Rajjuh and Abdel-Salam Salameh.
They join a businessman, Hassan Abdullah al-Nuri, and independent MP and former communist Maher al-Hajjar as candidates.
The candidates are mostly unknowns, with few details immediately available about their backgrounds or political leanings.
In northern Aleppo meanwhile, the Syrian Observatory for Human Rights said a mortar attack by rebels on government-held parts of the northern city killed at least 21 people.
Rebels also blew up a building in a government-held part of the Old City there that housed regime troops, the Britain-based monitoring group said.
It also reported regime air raids with explosive-packed barrel bombs on several opposition neighbourhoods in the east of the city, which killed at least six people.
In the east of the country, Iraqi helicopters hit a jihadist convoy on Sunday killing at least eight militants, said a spokesman for the interior ministry in Baghdad.
"The army struck eight tanker trucks in Wadi Suwab inside Syrian territory as they were trying to enter Iraqi territory to provide the (jihadist) Islamic State of Iraq and the Levant (ISIL) with fuel," Brigadier General Saad Maan said.
He said the strike was not coordinated with Syria's government.
The vehicles were travelling towards the western Iraqi border province of Anbar, where ISIL has been battling Iraqi security forces and where militants have seized the town of Fallujah.