Hillary Clinton
Hillary ClintonIsrael news photo: Flash 90

US Secretary of State Hillary Clinton said Thursday she is "betting against" Syrian President Bashar al-Assad's staying in power.

"The strategy followed by the Syrians and their allies is one that can't stand the test of legitimacy or even brutality for any length of time," Clinton told.

"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 added.

"It is clear to me there will be a breaking point," Clinton said. "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."

Clinton's remarks were made after a reporter asked her about Russia and China, which have blocked UN Security Council resolutions designed to end the violence in Syria.

"The pressure will build on countries like Russia and China because world opinion is not going to stand idly by. Arab opinion is not going to be satisfied watching two nations, one for commercial reasons one for commercial and ideological reasons, bolstering a regime that is defying every rule of modern international norms," she said.

She added that the "brutality" of Syrian President Bashar al-Assad's regime against its own people was "unsustainable in the internet age."

"When Assad's father conducted his horrific attacks back in the early '80s, there was no Internet, there was no Twitter, there were no social communication sites. There was no satellite television," Clinton said.

"It's much harder, and thankfully so, to have that level of brutality - shelling with artillery your own people - not be known by everyone, most particularly your own people, not after the fact but in real time," she added.

"In the event that he continues to refuse, we think that the pressure will continue to build," she said. "So it's a fluid situation. But if I were a betting person for the medium term and certainly the long term, I would be betting against Assad."

Her remarks came as Assad's forces shelled rebel-held districts of the flashpoint city of Homs for the 20th straight day on Thursday. Hundreds have been killed in Homs, a focal point of unrest, in recent weeks.

Residents of Homs fear Assad plans to follow in his father's footsteps of his father Hafez whose father put down a rebellion in Hama 30 years ago, killing at least 10,000.

The violence in Homs is only the latest in over a year of bloody crackdowns by Assad that UN Human Rights officials say has claimed at least 5,400 civilian lives.

However, UN officials stopped counting saying pervasive chaos in Syria made an accurate accounting impossible. Independent human rights group say the death toll now exceeds 7,300.

In London for an international conference aimed at finding ways to solve two-decades of pervasive blight and unrest in Somalia, Clinton is next headed for a gathering of Western and Arab powers on Friday in Tunis.

The Tunis "Friends of Syria" meeting is expected to be attended by more than 70 nations and international groups. It is unclear what steps would be undertaken in Tunis, but it is widely expected a push to close gaps in sanctions on Damascus in Asia, Eastern Europe, and Russia will be made.

However, US officials on Tuesday did say arming Syria's rebels could "become an alternative." It is unknown whether the meeting in Tunis will address arms, but observers say it is unlikely.

Russia, long-wary of regime change and protecting tens of billions of dollars in trade with Syria, said it will not attend the Tunis meeting.