Syrian forces used non-lethal chemical weapons against rebels in the town of Homs in late December, Le Monde has claimed.
The weapons were used in four rockets fired on December 23, according to unnamed sources in Western intelligence services cited by Le Monde. The newspaper suggested Western powers played down an isolated event in the hope it would not be repeated.
A French diplomatic source contacted by Reuters said Lalliot's response to Le Monde remained the official line.
The paper said Western powers had previously warned that recourse to chemical weapons could force them into action in a deadly conflict where President Bashar al-Assad has used troops to crush an uprising now nearly two years old
"We checked this out, closely, and notably the videos that were circulating. We cannot say that combat gas or any lethal chemical products were deployed," Le Monde quoted Lalliot as having told it of the chemical weapons reports.
The diplomatic source contacted by Reuters said this was and remained the case.
The United Nations says 60 000 have been killed in the 22-month-old conflict.
'Unacceptable' to discuss Assad's future
Syria's foreign minister said on Saturday any discussion of al-Assad's future was "unacceptable", a week after an international envoy said the president should not be part of a transitional government.
Foreign Minister Walid al-Moualem's comments showed the government has dug in against foreign pressure for a deal with the rebels fighting to topple Assad.
"No one should dare discuss the position of the president ... this is unacceptable," he told Syrian state television in an interview.
World powers have been deadlocked in their efforts to promote a transitional government they hope could prevent more bloodshed in the 22-month-old uprising against Assad.
Syrian officials condemned his comments and said the mediator was biased toward governments supporting the rebels.
Moualem said Assad's proposal earlier this month for a new Parliament and Constitution was the only way forward out of the conflict. He reiterated the embattled leader's argument that only "nationalistic opposition" could participate.
Their definition excludes the armed opposition or any group that supports intervention in Syria's conflict, even though they are now the driving force of the rebel movement.
The opposition, for its part, has rejected anything but Assad's removal.
International talks in Geneva last June, led by Brahimi, proposed a transitional government but left open Assad's future. The proposal foundered after opposition backers like the United States insisted Assad not play a role, while Russia, Assad's main arms supplier, said foreign powers should not impose restrictions on the transition. - Reuters