US president Barack Obama has declared Syria's main opposition group the sole "legitimate representative" of its country's people, deeming the move "a big step" in the international diplomatic efforts to end Syrian president Bashar Assad's regime.
Mr Obama said the newly formed Syrian Opposition Council "is now inclusive enough" to be granted the elevated status, which paves the way for greater US and international support for the organisation.
"Obviously, with that recognition comes responsibilities," the US president said in an interview with ABC News, "to make sure that they organise themselves effectively, that they are representative of all the parties, that they commit themselves to a political transition that respects women's rights and minority rights."
Recognition of the council as the sole representative of Syria's diverse population brings the US in line with Britain, France and several of America's Arab allies, which took the same step shortly after the body was created at a meeting of opposition representatives in Qatar last month.
Mr 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 could use or lose control of its stockpile of chemical weapons.
US defence secretary Leon Panetta said the Syrian government seems to have slowed preparations for the possible use of chemical weapons against rebel forces. Last week, US officials said there was evidence that Syrian forces had begun preparing sarin, a nerve agent, for possible use in bombs.
"At this point the intelligence has really kind of levelled off," Mr Panetta told reporters travelling with him to Kuwait, where he will visit US troops at the start of a four-day trip. We haven't seen anything new indicating any aggressive steps to move forward in that way."
US recognition of the opposition council is expected to be a centrepiece of an international conference on the Syria crisis in Morocco. Secretary of state Hillary Clinton had been due to attend today's meeting in Marrakech but cancelled her trip because she was ill with a stomach virus, her spokesman, Philippe Reines, said. Instead, deputy secretary of state William Burns will lead the US delegation.
On Monday, Ms Clinton designated Jabhat al-Nusra, or "the Support Front" in Arabic, a foreign terrorist organisation. The move freezes any assets its members may have in US jurisdictions and bars Americans from providing the group with material support.
The designation is largely symbolic because the group is not thought to have holdings or support in the United States, but officials hope the penalties will encourage others to take similar action and discourage Syrians from joining. That step was part of a package intended to help the leadership of the Syrian Opposition Council improve its standing and credibility as it pushes ahead with planning for a post-Assad future.