U.N. Secretary-General Ban Ki-moon has named Swedish scientist Ake Sellstrom to head a U.N. investigation into allegations that chemical weapons were used in Syria, Ban's spokesman said on Tuesday.

"He is an accomplished scientist with a solid background in disarmament and international security," U.N. spokesman Martin Nesirky said.The United Nations said last week it would investigate Syrian allegations that rebels used chemical arms in an attack near the northern city of Aleppo, but Western countries sought a probe of all claims about the use of such arms, including rebel charges that government forces used them.

If an investigation adds credibility to the rebels' claims that the government has used chemical weapons, it would represent another blow to Bashar al-Assad's efforts to retain power. If it turned out the rebels have used them, it could make countries even more reluctant to support the opposition.

It was not immediately clear who else would be on Sellstrom's team. Russia said on Monday that Russian and Chinese experts should be part of the investigation, but Moscow's U.N. Ambassador Vitaly Churkin said on Tuesday that Russia would "most likely not" be represented.

Sellstrom was a chief inspector for UNSCOM, the U.N. inspection team that investigated and dismantled Iraq's biological and chemical weapons programs in the 1990s.Sellstrom also worked with UNMOVIC, the U.N. group that returned to Iraq in 2002 and found no solid evidence that Baghdad had revived its weapons-of-mass-destruction programs before the 2003 U.S.-led invasion as Washington and London alleged at the time.

Nesirky said Sellstrom's investigation would be a technical, not a criminal, investigation, looking at whether chemical weapons were used and not at who may have used them.

U.S. and European officials say there is no evidence of a chemical weapons attack, but the allegations of the rebels are worth taking seriously. If one were to be confirmed, it would be the first use of such weapons in the two-year-old Syrian conflict, which the United Nations says has cost 70,000 lives.

France and Britain wrote to Ban on Thursday to draw his attention to rebel allegations of an attack near Damascus, as well as one in Homs in late December. The rebels blame Syria's government for those incidents as well as the Aleppo attack.

EXPANDING THE INVESTIGATION?

Ban made clear on Thursday that the investigation would initially focus on the Aleppo incident, in which the government and rebels accuse each other of firing a missile laden with chemicals, killing 26 people.

But he has left open the possibility that the investigation could be broadened. In a letter to the Security Council on Friday, Ban said he had asked Britain, France and Syria for further information on the other alleged chemical attacks "with a view to verifying any alleged use of chemical weapons in Syria."

Britain's U.N. Ambassador Mark Lyall Grant told reporters on Tuesday that he has provided Ban's office with "further information" about the alleged chemical attacks in Syria. He declined to provide details.The suggestion that the investigation may go beyond the Aleppo attack has infuriated Russia. Security Council diplomats told Reuters on condition of anonymity that the Russian U.N. mission went so far as to ask Ban to withdraw his Friday letter.

Russia's U.N. mission had no response on Monday when asked to comment on the alleged request that Ban withdraw his letter. Russian Ambassador Vitaly Churkin said on Monday that the Anglo-French call for a broader investigation was an attempt to "delay and possibly derail" the U.N. probe.

Russia has criticized Western and Arab calls for Assad to leave power and, together with China, has blocked three U.N. Security Council resolutions meant to pressure him to end violence. It has also differed with the West over which side was to blame for alleged massacres and other atrocities in Syria.A member of the Syrian opposition said Sellstrom's investigation would not be hindered by the rebels.

"We can guarantee him (Sellstrom) safe passage in the areas where the incidents took place in northern Syria," Wael Merza, an adviser to the Syrian coalition's new interim Prime Minister Ghassan Hitto, told Reuters on sidelines of an Arab summit in Doha.Merza said there were at least two known cases where they suspect chemical weapons were used by forces loyal to Assad.