Syria has not yet agreed to give the "unfettered access" demanded by the United Nations for an inquiry into the alleged use of chemical weapons in the country's conflict, diplomats said Wednesday.
The United Nations wants the team to start work as early as next week but has still not reached an agreement with President Bashar al-Assad's government on the extent of the investigation, diplomats and UN officials said.
The Syrian government has asked the UN to investigate its accusation that opposition rebels used chemical weapons in Aleppo province.
Britain and France have demanded that the inquiry also take up opposition demands that the government staged that attack and other two other allegations that the government used chemical weapons.
UN leader Ban Ki-Moon on Tuesday named Swedish scientist Ake Sellstrom, a veteran of 1990s arms investigations in Iraq, to head the inquiry.
Ban has repeatedly demanded that the physics, chemical and health experts be given "unfettered access" in Syria to determine whether chemical weapons have been used in the two-year-old conflict.
"The government has still not given this pledge. This will be the key to whether the mission can start, but it is too early to say yet that it will be called off," a UN diplomat told AFP.
"There are discussions going on ... about the terms of reference," UN spokesman Martin Nesirky told reporters.
"It is obvious that to be able to do this work, you need unfettered access and that is why the secretary general has underscored that in his communications," Nesirky said.
The UN wants between eight and 10 experts suggested by the Organization for the Prohibition of Chemical Weapons (OPCW) to carry out the inquiry, diplomats said. Syria is not a member of the Chemical Weapons Convention and is believed to have a large stock of sarin and other nerve gases.
"Paramount importance is being attached to obtaining assurances regarding the safety and security of the OPCW personnel to be deployed," OPCW director general Ahmet Uzumcu told the organization's executive council in The Hague on Wednesday, said a spokesman.
The team would be based in Beirut and "the UN hopes to have them in place next week," a second western diplomat said.
Ban does not want experts from the Security Council permanent members -- Britain, China, France, Russia and the United States -- on the team because of the political sensibilities, diplomats said.
No experts from Turkey or Arab countries are expected to take part for the same reasons. Most of the experts are expected to come from Latin American, European Nordic and Asian countries, diplomats said.
Syria asked for an investigation last week into its allegation that the opposition used chemical weapons near the city of Aleppo on March 19.
Britain and France have demanded that the inquiry also look into opposition accusations that the government used chemical arms in the Aleppo attack and near Damascus on March 20.
The UN has said that the "initial focus" of the inquiry will be the Syrian government allegations. But Ban's statements have left open the possibility of extending the mandate.
The UN has stressed that the inquiry is only to determine whether chemical weapons have been used, not by who. "It is not a criminal investigation," Nesirky said.
The Western diplomat said that if chemical weapons were used, it was "low-level".
The official said government forces "may be trying to test out low-level chemical weapons to see whether there will be an international reaction, to see whether this hits any red lines."