DAMASCUS, Syria (AP) -- The head of an international mission to Syria charged with destroying the country's chemical weapons called on President Bashar Assad's government Sunday to ensure it meets a deadline to destroy all its toxic chemicals amid a raging civil war.
Also Sunday, four more candidates announced their candidacy for Syria's upcoming June presidential election, state television announced, a poll Assad is expected to win.
Meanwhile, clashes raging through the northern city of Aleppo killed at least 20 people and wounded over 50, activists reported.
Sigrid Kaag of the Organization for the Prohibition of Chemical Weapons told reporters in Damascus that 92.5 percent of Syria's chemical materials had been removed from the country and destroyed. She called it "significant progress," although she called on Syria's government to ensure remaining materials would be eradicated by the end of April.
"I strongly encourage (the Syrian government) to go for that last push that we can really talk of hundred percent removal and destruction," Kaag said.
Syria missed an April 13 deadline to destroy all its chemical weapons in accessible locations. International experts say that could impact on reaching a June 30 deadline to remove all Syria's chemical weapons.
"An important (achievement) has been made in permanently closing down production facilities," Kaag said, adding it came in "a very short period of time and under difficult and challenging security conditions."
Another 12 chemical weapons production facilities are still being reviewed by the OPCW to see how they will be destroyed, she said.
She said the timely removal of toxic chemicals had become even more pressing to ensure "none of the chemical weapons material falls in the wrong hands," referring to rebels trying to overthrow Assad who include the increasingly influential al-Qaida-linked Nusra Front.
She said fighting in areas where sensitive sites were located could rapidly deteriorate, making a "timely and swift extraction even more" important.
Syrian officials did not comment on Kaag's remarks.
The international community aims to remove and destroy 1,300 metric tons of chemicals Syria stockpiled to turn into poison gas and nerve agents.
The effort was sparked by an Aug. 21 chemical weapons attack near Damascus that killed hundreds of people. The attacks were blamed on Assad's government and brought the United States to the brink of military intervention in Syria. Damascus denied involvement.
In recent weeks, activists have accused government forces of attacking rebel-held areas with poisonous chlorine gas, according to Associated Press interviews with more than a dozen activists, medics and residents on the opposition side.
Syria denies the allegations, and they haven't been confirmed by any international organization.
Kaag acknowledged the reports of renewed chlorine gas attacks but said they were so far "unsubstantiated allegations."
She said the OPCW's technical secretariat had contacted the Syrian government over the allegations, but gave no further details.
If the allegations are true, they highlight the limitations of the global effort to rid Syria of toxic material.
Meanwhile, Sawsan Omar Haddad, a 51-year-old engineer from the coastal province of Latakia, became the first woman to register as a candidate in Syria's upcoming June 3 presidential election.
In a state television broadcast Sunday, parliament speaker Jihad Laham said Haddad had registered her candidacy a day earlier.
Another three candidates also registered Sunday, bringing the total number of contenders to six.
The other three who registered Sunday were Samir Ahmed Moalla, a 43-year professor of international law from the southern province of Quinetra; Mohammad Firas Rajjouh, 48, from Damascus; and Abdul-Salam Salameh, 43, from the central province of Homs.
Assad has suggested he would seek a third, seven-year term, though he has not announced his candidacy yet.
Analysts said they expected at least one candidate to run against Assad to give the election a veneer of legitimacy.
Syria's opposition have blasted the decision to hold presidential elections amid the country's 3-year-old conflict, which has killed more than 150,000 people and driven a third of the country's population from their homes.
Syria's foreign ministry rejected the criticism, saying the decision to hold presidential elections was "sovereign." It warned that "no foreign power will be allowed to intervene" in the process.
Also Sunday, at least 24 people were killed and more than 50 wounded in fighting between pro-Assad forces and rebels in the northern city of Aleppo, reported the Britain-based Syrian Observatory for Human Rights.
The fight for Aleppo is particularly important now, with analysts saying they expect Assad's forces will try wrest as much of the city as possible before elections.