The United Nations on Tuesday named a Swedish scientist to lead an inquiry into the alleged use of chemical weapons in Syria, but has barred experts from the major powers from taking part, officials said Tuesday.

UN leader Ban Ki-Moon appointed Ake Sellstrom of Sweden, a veteran of 1990s arms investigations in Iraq, to head the inquiry. No definitive mandate for the inquiry has been announced, although the UN said the aim is not to find who staged the alleged attacks.

Ban has told the UN Security Council permanent members -- the so-called P5 of Britain, China, France, Russia and United States -- that they will not be allowed to take part, diplomats said.

The decision was taken because of divisions over the worsening two-year-old war between President Bashar al-Assad's forces and opposition rebels, diplomats said.

Russia, Assad's main international backer, has made clear its irritation at being excluded. Russia expressed its "willingness" to take part in the investigation, Russia's UN ambassador, Vitaly Churkin, told reporters.

"We were told that the secretariat preferred to have a team which would exclude P5 members," he added.

"We do not fully share this kind of attitude but the main thing is for it to be as objective a team as possible," Churkin said. "So we will see what kind of group that will be and what will be the results of their work."

Syria asked for an investigation last week into its allegation that the opposition used chemical weapons in Aleppo on March 19. Britain and France have demanded that the inquiry also look into opposition accusations that the government used chemical arms in Aleppo and near Damascus.

Russia has strongly backed the Syria demand that the investigation be limited.

The UN has only said that the "initial focus" of the inquiry will be the Syrian government allegations.

UN spokesman Martin Nesirky said "the terms of reference for the mission are being finalized," including the composition of the inquiry team. No timetable has been set for the work to start.

"It is not a criminal investigation, it is a technical mission," said Nesirky. The investigators will be "aimed at ascertaining whether chemical weapons were used and not by whom."

Sellstrom, the head of the inquiry, is currently senior researcher at the European Center for Advanced Studies of Societal Security and Vulnerability, specializing in major incidents with chemical, biological, radiological, nuclear and explosive substances.

A renowned expert on disarmament and international security, Sellstrom was chief inspector with the UN Special Commission (UNSCOM) and also top adviser to the UN Monitoring, Verification and Inspection Commission (UNMOVIC) for Iraq.

He has taught at US universities and was also director of the Swedish Defense and Security Research Institute.