The United States is set to call for tough new UN sanctions against President Bashar al-Assad and his inner circle, as over 100 Western and Arab nations meet Friday in Paris for "Friends of Syria" talks.

But despite the more than 16,500 people estimated killed in the 16-month uprising against Assad's regime, key Syria allies Russia and China - which both hold UN veto rights - are not attending despite reports of changing attitudes in Moscow.

The Paris meeting follows a gathering in Tunis and another in Istanbul, both of which called in vain for tougher action against Assad's government.

China did not attend either of those meetings, in which the United States, France, Britain, Germany and Arab nations Saudi Arabia and Qatar led a group of more than 60 members, including most EU states and many Arab League nations.

The United States will lead calls at the Paris talks for a tough new UN sanctions regime to be imposed on Assad and his inner circle, Washington
officials said Thursday.

Speaking as US Secretary of State Hillary Clinton flew to Paris for the Friends of Syria meeting, one official said it was time "to put this all together under a Security Council resolution that increases the pressure on Assad, including having real consequences" such as economic sanctions.

"We, and we believe most of the countries represented in Paris, think that has to include Chapter 7 economic sanctions on Assad," the official said aboard Clinton's plane and asking to remain anonymous, referring to a clause within the UN charter.

"Many of the countries in Paris already have those sanctions but globalising them will be very important. That is the argument that we will continue to make to Russia and China."