LONDON - US Secretary of State Hillary Clinton suggested on Thursday Syria's opposition will ultimately arm itself and said she would bet against Syrian President Bashar Assad's staying in power.Speaking directly to Russia and China, which have blocked UN Security Council resolutions designed to end the violence in Syria, Clinton said the government's "brutality" against its own people was unsustainable in the Internet age.For more than a year the Syrian opposition has called for Assad, whose family has ruled Syria for four decades, to step down in the latest of the "Arab Spring" uprisings against authoritarian rulers in the Middle East.The continued strife reflects both Assad's determination to remain in office as well as the major powers' inability to agree on a strategy on whether to try to ease, or force, him out.Russia has said it will not attend the gathering in Tunis.Russia has repeatedly said it does not want a resolution to become a pretext for regime change, something it believes took place when the Security Council authorized the use of force to protect civilians in Libya and that ultimately helped drive former dictator Muammar Gaddafi from power.Clinton, however, suggested Russia and China may not be able to sustain their opposition for ever."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 added.BETTING AGAINST ASSADResidents of Homs fear Assad will subject the city to the same treatment his late father Hafez inflicted on the rebellious town of Hama 30 years ago, when 10,000 were killed."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. There were no on-the-ground witnesses," 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.Clinton did not provide details about what the United States and its Arab and European allies might do if Assad refused to let humanitarian aid in, though she spoke of tightening existing sanctions and possibly considering new ones."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."US officials avoided answering questions on whether the "Friends of Syria" group may discuss the possibility of arming the opposition, something some nations favor and that the United States, in a change in emphasis, on Tuesday suggested could become an alternative."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 reporters in London."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. 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."Speaking ahead of a gathering of Western and Arab powers on Friday, US officials separately said the group planned to challenge Assad to provide humanitarian access within days to civilians under assault by his forces.The officials, speaking before a "Friends of Syria" meeting expected to gather more than 70 nations and international groups in Tunis, did not say what specific consequences would follow if Syrian authorities failed to provide access.The Syrian military pounded rebel-held Sunni Muslim districts of Homs city for the 20th day on Thursday, despite international protest over the previous day's death toll of more than 80, including two Western journalists, activists said."One of the things you are going to see coming out of the meeting tomorrow are concrete proposals on how we, the international community, plan to support humanitarian organizations ... within days, meaning that the challenge is on the Syrian regime to respond to this," said a US official.