In an English translation provided by the State Department, Clinton wrote under the headline "There Is No Going Back in Syria" that it was "increasingly clear" the crackdown was an irreversible shift in the country's push towards reform.
The Syrian regime's "continued brutality may allow (President Bashar al-Assad) to delay the change that is under way in Syria, it will not reverse it," Clinton wrote in the pan-Arab daily published in London.
"The most important question of all - what does this mean for Syria's future? - is increasingly clear: There is no going back."
The top US diplomat rejected Syrian government claims that the protests were largely the work of foreign forces.
The Syrian people, she wrote, "are demanding their long-denied universal rights and rejecting a government that rules through fear, squanders their talents through corruption, and denies them the dignity of having a voice in their own future."
More than 1,200 people have died and some 10,000 have been detained in Syria since the mid-March eruption of pro-democracy protests inspired by the uprisings that toppled long-standing rulers in Egypt and Tunisia.
Assad's actions have "shattered his claims to be a reformer," Clinton wrote, criticizing the Syrian leader for following the example of repression set in Iran.
A senior US administration official said Friday that the United States was studying whether war crimes charges could be brought against Syria to pressure its regime to end a bloody crackdown on dissent.
Two administration officials, speaking on condition of anonymity, outlined the campaign in a teleconference with reporters, stressing that efforts were being made at the United Nations and with partners in the region to condemn and isolate the regime.
The official said other measures, including sanctions targeting the country's oil and gas sector, were being considered as part of a broader diplomatic campaign to increase pressure on Assad.
"Syria is headed toward a new political order - and the Syrian people should be the ones to shape it," Clinton wrote, noting that Washington "chooses to stand with the Syrian people and their universal rights."
President Barack Obama has previously called on Assad to either lead a transition to democratic rule or "get out of the way," though he has come under fire from some in Congress for not taking a tougher stance.
Copyright APP (Associated Press of Pakistan), 2011
Copyright AFP (Agence France-Presse), 2011