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The Obama administration's top diplomat suggested Tuesday that the Arab Spring has entered difficult and uncharted territory between dictatorship and democracy, and that some changes would have to come slowly.

In an interview with The Associated Press, Secretary of State Hillary Rodham Clinton said the United States would continue to pressure long-time leaders to leave power in Syria and Yemen, and ensure chaos is averted in Egypt, where demonstrators have succeeded in ousting an autocrat. But she cautioned against overly optimistic forecasts for how quickly each country could make its break with the past.

"How long? When?" Clinton said about possible regime change in Syria. "I cannot predict these to you."

The message was similar for ending Yemen's civil strife as for ensuring that Egypt makes a successful transition in its post-Hosni Mubarak era toward real democracy. She said each country faces difficult challenges.

On Syria, she voiced support for the burgeoning opposition against the regime of Syrian President Bashar Assad, but said the primarily Sunni protesters "have a lot of work to do internally" toward becoming a truly national opposition movement that also represents the aspirations of Syria's minorities.

"It is not yet accepted by many groups within Syria that their life will be better without Assad than with Assad," Clinton said. "There are a lot of minority groups that are very concerned."

She urged the anti-Assad camp to maintain the "moral high ground" of nonviolence and reach out to Syria's minorities, and expressed optimism that the tide was turning against Syria's government.

She pointed specifically to last week's assassination of Mashaal Tammo, a Kurdish opposition leader. Tammo's son has since called on members of his ethnic group to join the 7-month uprising against the Assad regime, and Clinton predicted a similar shift from Druze, Christians, business leaders and other groups who have so far been reluctant to join the revolution.

Tammo's killing "seems to have been just a spark to the tinder because that goes right at one of those groups that up until now had been kind of on the sidelines," she said. "As this goes on, I really believe there will be more support for change."

But the U.S. cannot speed that process along. "It cannot be accelerated from the outside," Clinton told the AP. "The single message that comes through loudly and clearly from everyone associated with the opposition is that they do not want foreign intervention."

Clinton suggested the U.S. was facing a similar period of waiting with Yemen, where American, Arab and European officials are trying to persuade President Ali Abdullah Saleh to leave power.

Eight months of mass protests has evolved into an armed standoff between government and opposition forces, though Clinton said the situation hasn't descended into an all-out civil war. Saleh, in power since 1978, recently returned from three months of treatment in Saudi Arabia after being severely wounded in an attack on his presidential palace, and has offered no concrete indication that he is willing to step down.

Saleh "is clearly not ready to go, and the demonstrators are not ready to leave, and Al-Qaida is trying to take advantage of it," Clinton said. The U.S. message to Yemen, she added, was "regardless of where you come and who you are, you need a fresh start and you need a new leader. And then you need a fair process for choosing the next leader, and we can help you do that."

However, "this is also going to take some time," Clinton warned.

On a day when U.S. officials focused on the threat posed by Iran, announcing that a terror plot to assassinate Saudi Arabia's ambassador in Washington had been foiled, Clinton also expressed deep concern about the deaths of 26 Egyptians last weekend in the worst violence since the February fall of Hosni Mubarak. She said the sectarian nature of the unrest was worrying.

Videos show military armored vehicles plowing through Christian protesters, and activists accuse the interim leadership of fomenting sectarian hatred as a way to end protests and halt criticism of their guidance of the country's post-Mubarak transition.

The ruling military has to focus on advancing Egypt's democracy and re-establishing stability, Clinton said. The U.S. is keeping a "constant channel of communication" open with Egyptian authorities, who need to "find out what happened and take steps to prevent it from happening again," she explained.

Clinton spoke earlier Tuesday by telephone with Egypt's Foreign Minister Muhammed Amr, and she said she urged his government to investigate the violence and the role that state media played in "fanning the flames." She said Egypt's government should grant Coptic Christians protection from religious discrimination and the right to build churches — a law it has discussed but never enacted.

Egypt's government, like much of the region, is in "new territory," Clinton conceded: "Sometimes they don't know what's going to happen next because this is something they didn't sign up for."

In such a situation, she said as Americans "we have to try to keep our voice in the mix."

"When we talk about elections, when we talk about building a democratic government, it's not just holding an election," Clinton said. "We hope that they will get back to protecting peaceful assembly, freedom of worship, the kinds of basic rights that make up democratic values."