U.S. Secretary of State Hillary Clinton said on Thursday the Syrian National Council (SNC) was a "credible representative" of the country's opposition, ahead of a meeting in Tunisia of the "Friends of Syria" group, Al Arabiya reported.
"The consensus opinion by the Arab League and all the others who are working and planning this conference is that the SNC is a credible representative and therefore they will be present" at a meeting in Tunis on Friday, she said.
Clinton said that the Syrian opposition will become increasing capable and find the means to launch attacks.
"There will be increasingly capable opposition forces. They will from somewhere, somehow find the means to defend themselves as well as begin offensive measures," she told reporters after taking part in a London conference on Somalia, according to Reuters.
"It is clear to me there will be a breaking point. I wish it would be sooner, so that more lives would be saved, than later, but I have absolutely no doubt there will be such a breaking point," she said.
The White House, meanwhile, branded Syrian President Bashar al-Assad's assault on his own people as "heinous and unforgivable," following another violent day in the besieged nation.
"That's why we're working with a broad array of international partners to isolate and pressure Assad, to bring around a peaceful transition in that country," spokesman Jay Carney told reporters traveling with President Barack Obama, AFP reported.
Asked if Obama had seen images of the violence in Syria, Carney replied: "I know he is fully aware, has been briefed on and read many news accounts about the atrocities committed by the Assad regime. It is the reason why he has so forcefully condemned it."
The remarks came after an international panel handed to the U.N. a list of Syrian officials suspected of crimes against humanity, and as the regime in Damascus ignored an outcry over the killing of two western journalists.
The panel said there had been a widespread and systematic pattern of gross violations committed by Syrian forces, "in conditions of impunity," since March 2011 when the uprising against Assad's regime erupted.
The report said Syria's government had "manifestly failed" to protect its people, but also said it had found instances of gross abuses committed by rebel fighters, many of them army defectors.
Activists spoke of "terrifying explosions" in the besieged city of Homs, as encircling troops pounded rebel areas for a 20th straight day.
Kofi Annan favorite for Syria post
Meanwhile, diplomats said that former U.N. secretary general Kofi Annan was the favorite to become the international envoy on the worsening Syria crisis.
Annan and former Finnish president Martti Ahtissari were the two leading candidates to be the envoy, diplomats said. Two top Arab officials are also being considered.
Current U.N. chief Ban Ki-moon will speak with Annan on Thursday amid growing pressure for an initiative on the conflict which has left thousands dead, U.N. officials said on condition of anonymity as the talks were confidential.
Annan was secretary general from 1997 to 2006. He has since been called upon to mediate in troubles such as unrest in Kenya that erupted in 2008.
CNN television, citing "a senior U.N. source," reported in a Twitter message that the post would go to Annan.
Annan and Ahtissari, who was the U.N. envoy on the Kosovo conflict, are both Nobel peace prize winners.
Also being considered are Mouloud Hamrouche, a former prime minister of Algeria, and Mohammed Sabah al-Salem al-Sabah, a former foreign minister for Kuwait, diplomats said.
Ban held consultations on the appointment while at an international conference on Somalia in London. Officials said no official announcement was expected on Thursday however, according to AFP.
The U.N. leader met European Union foreign affairs representative Catherine Ashton, Arab League secretary general Nabil al-Araby and the Organization of Islamic Cooperation chief Ekmeleddin Ihsanoglu to discuss the special envoy, said U.N. spokesman Martin Nesirky.
"They also discussed the humanitarian crisis in Syria" and a planned mission to Syria by U.N. humanitarian chief Valerie Amos, said Nesirky.
The international community has been badly divided on the Syria crisis. Russia and China vetoed two U.N. Security Council resolutions condemning the bloodshed.
But since the U.N. General Assembly passed a symbolic resolution last week, Russia has stepped up calls for greater efforts on easing deteriorating humanitarian conditions in Syria.
More than 7,600 people have been killed in the 11 months since the uprising against President Bashar al-Assad's government began, the British-based Syrian Observatory for Human Rights says.