The fourth conference for the "Friends of the Syrian People" was set to open Wednesday after the U.S. said the new Syrian opposition coalition is the "sole legitimate representative" of the Syrian people.
The U.S. move, announced by President Barack Obama late Tuesday, follows that of France and the U.K. and what that will mean for the Syrian opposition should be indicated by the results of the conference, which includes more than a hundred delegates from Europe and the Gulf countries in the Moroccan city of Marrakech.
The Syrian National Coalition, formed in November during a conference in Doha, Qatar, has been calling for increased international support, including military material for opposition forces battling the regime of Bashar Assad in Syria for nearly two years.
The U.S. is not, however, expected to approve military aid, in part over fears of al-Qaida linked rebel units operating in the country.
Obama's announcement follows his administration's blacklisting of a militant Syrian rebel group with links to al-Qaida. That step is aimed at blunting the influence of extremists amid fears that the regime may use or lose control of its stockpile of chemical weapons.
The U.S. had been leading international efforts to prod the fractured Syrian opposition into coalescing around a leadership that would represent all of the country's factions and religions. Yet it had held back from granting recognition to the group until it demonstrated that it could organize itself in credible fashion.
In particular, Washington had wanted to see the group set up smaller committees that could deal with specific immediate and short-term issues, such as governing parts of Syria under their control and putting in place institutions to address the needs of people once Assad is ousted. Some of those committees could form the basis of a transitional government.
U.S. Secretary of State Hillary Rodham Clinton was expected to attend the conference, but cancelled following an illness and will be represented by Deputy Secretary of State for the Middle East, William Burns.
Russian Foreign Minister Sergey Lavrov said Wednesday the recognition contradicted earlier international agreements that foresee the "commencement of an all-Syria dialogue" that would include all sides of the conflict, in which more than 40,000 people have died so far.