France said on Friday that it was unlikely for now that a no-fly zone would be established over Syria because of opposition from some members of the UN Security Council.

Western diplomats say the United States is considering imposing a no-fly zone close to Syria's southern border with Jordan.

"The problem with this type of measure is that it can only be put in place with approval from the international community," French Foreign Ministry spokesman Philippe Lalliot told journalists.

"A decision from the United Nations Security Council is needed, and not just any decision," he said. A Chapter 7 resolution authorizing military action was needed, and that was unlikely to be passed, he added.

The government of Syrian President Bashar al-Assad can count on Moscow to block any such resolution if it were to be brought to a vote.

US President Barack Obama's administration said on Thursday that it was ready to arm Syrian rebels after having obtained proof that the government had used chemical weapons against the fighters seeking to oust Assad.

Lalliot said France had yet to make a decision on arming rebels, but that all these issues would be discussed among heads of state at next week's G8 summit.

Apart from arming the rebels, France could also extend further help to them in the form of sharing more intelligence, providing training and planning operations, Lalliot added.

He declined to say whether that meant French military advisers would be on the ground in Syria, although diplomatic sources have indicated some are already operating in Turkey and Jordan.

President Vladimir Putin's senior foreign policy adviser said on Friday that information that the US has given Russia about suspected use of chemical weapons by Syrian President Bashar al-Assad's forces "does not look convincing".

Yuri Ushakov said more US military support for Assad's opponents would undermine joint efforts to bring together Syrian government and opposition representatives for peace talks.

But he said Russia was "not yet" considering sending Assad advanced missiles in response and voiced hope for constructive talks between Putin and Western leaders at a G8 summit next week, saying Moscow and Washington do not "compete" over Syria.

Syria's foreign ministry said the US was lying about chemical weapons use to give it an excuse to intervene in the country's two-year-old civil war.