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Opposition leader Aung San Suu Kyi cautioned Thursday that the democratic reforms started by Myanmar's nominally civilian government are not "unstoppable" and will succeed only if the powerful military accepts the changes.

The Nobel Peace Prize laureate said she is cautiously optimistic more progress can be made.

Her comments in an interview with The Associated Press were clearly meant to caution the West not to get carried away by the reforms and to remind it that Myanmar's long-ruling military still wields enormous power despite a veneer of democracy provided by the elections.

"I wouldn't say that there are many dangers, but I wouldn't say that it is unstoppable either. I think there are obstacles, and there are some dangers that we have to look out for," Suu Kyi said.

"I am concerned about how much support there is in the military for changes. In the end that's the most important factor, how far the military are prepared to cooperate with reform principles."

She spoke as she and her National League for Democracy moved closer to full participation in mainstream electoral politics. The government approved the party's registration Thursday, and the NLD can now pick candidates to run in by-elections on April 1.

The party decided to rejoin electoral politics after the military-backed but elected government took office in March, replacing army rule and tentatively easing years of repression. Its changes included legalizing labor unions, increasing press freedom and opening a dialogue with Suu Kyi.

Critics have characterized the NLD's decision to rejoin electoral politics as a capitulation after years of resistance to military rule. The party won a 1990 general election but was denied power after the military refused to allow parliament to be seated. In 2010, the military held another general election, but the NLD found the rules unfair and declined to participate, leading to its being purged from the list of legal political parties.

The critics fear the NLD's participation helps the government maintain a veneer of legitimacy for what is actually -- by constitutional statute, as well as the majority held by pro-military lawmakers -- continued domination of politics by the army.

"I think this year we shall find out whether we are making progress toward democracy," Suu Kyi said, adding that benchmarks to consider are "the release of all political prisoners,... how the by-elections are conducted,... how much more freedom of information is allowed and whether strong steps are taken to establish the rule of law."

The release of political prisoners -- estimated to number between 600 and 1,700 -- is a touchstone for reformers and activists abroad.

Several mass amnesties for convicts have resulted in the release of more than 200 political detainees, but many high-profile prisoners still are serving long terms. The latest release on Tuesday met with particular disappointment, because hopes had been raised by the government's increased engagement with the NLD and foreign countries critical of the military, evidenced most notably by the December visit of U.S. Secretary of State Hillary Rodham Clinton. British Foreign Secretary William Hague is visiting this week, bringing the same message of encouraging reforms.

Hague is the first British foreign secretary to visit Myanmar since 1955. In meetings with President Thein Sein and other government officials in Naypyitaw on Thursday, he emphasized "the importance the British government attaches to the reforms that the Burmese government has undertaken in the last six months," he said in a statement released in London.

Britain continues to call Myanmar by its name under British rule, rather than the local government's official designation.

Though Hague's two-day visit signals a shift in relations, Britain won't promise any immediate change in European Union sanctions on arms sales, asset freezes and travel bans -- or change a policy that discourages U.K. businesses from trade with Myanmar.

He added Britain "expects to see the release of all political prisoners, credible by-elections in April, and a genuine alleviation of the suffering in ethnic areas."

Suu Kyi agreed that the failure to release more political detainees was "disappointing" but see the prisoners as the manifestation of a bigger problem, the "lack of rule of law," which means activists could be put away again for the flimsiest of reasons.

She said she feels there are differences among the authorities on who might actually pose a danger to society, opting for confrontation and causing unrest.

"I have always said it would be best to release everybody at the same time. Keeping some back does not really help. Nobody's grateful, everybody's disappointed if they release just a few," she said.

Suu Kyi said resolving the country's long-running ethnic conflicts is likely the more important issue over time, because "unless there is ethnic harmony it will be very difficult for us to build up a strong democracy." The country's sizable ethnic minorities have for decades struggled for greater autonomy, leading to cycles of brutal counterinsurgency war.

Although the previous military regime concluded cease-fires with many of the groups, the pacts have been precarious and some of the larger guerrilla armies never joined them. Despite an order by Thein Sein to cease hostilities, the military is engaged in a bloody struggle against the Kachin minority in the north, often overlooked because of its remote location and the positive developments nationally.

"The Kachin situation is important now because of the hostilities and the fate of the refugees and the local people," said Suu Kyi. But the conflict is also representative of relations between the government and ethnic nationalities all over the country, a problem that should be resolved by a political settlement, she said.

Suu Kyi is expected to run for a parliamentary seat, a decision her party will formalize later this month. Asked about the risk that she will be co-opted, specially holding a small minority of seats, she said the party will continue to work outside parliament.

"We mustn't forget that we have seen doing our work outside parliament, even when there was no parliament, for the last 20-something years. We will continue with our extra-parliamentary activities and what activities we undertake within the government are just an addition to the political work we have been doing for the past 23 years," she said.

She defended her decision to follow the electoral path: "I think it's very dangerous if so-called democratic politicians think they are above the electoral process."