U.S. President Barack Obama is calling Burma's decision to release hundreds of political prisoners “a substantial step forward for democratic reform.”

The Burmese government and democratic activists said 651 prisoners walked free on Friday as part of a mass amnesty that falls in line with demands made clear by U.S. Secretary of State Hillary Clinton during a visit last month.

In response, Clinton announced on Friday that the U.S. will start the process of exchanging ambassadors with Burma.

“This is a substantial and serious step forward in the government's stated commitment to political reform and I applaud it and the entire international community should as well.” 14;49

The prisoner's release fulfills a U.S. condition for mending diplomatic relations with the Southeast Asian nation.

But Mr. Obama and Clinton said in separate statements that more work needs to be done in Burma. The Obama administration urged the government to pave the way for free and fair elections in the country this year and to release the remaining political prisoners on a unconditional basis.

Burma's new military-backed government has been reaching out to the West and recently hosted both Secretary Clinton and British Foreign Secretary William Hague.

Hague on Friday said he welcomed the prisoner release, calling it a “further demonstration of the Burmese government's commitment to reform.”

Burmese state media said the detainees were freed under an amnesty ordered by President Thein Sein in order to foster national reconciliation.

Those freed included democracy activist Min Ko Naing – a key student leader of the failed 1988 uprising – and Shin Gambira, a well-known Buddhist monk who led street protests in 2007.

The military-backed government also released Shan ethnic minority leader Khun Htun Oo, who was serving a 93-year sentence on charges of treason, and former prime minister and intelligence chief Khin Nyunt.

The amnesty comes a day after the Burmese government signed a cease-fire deal with the ethnic Karen rebel group, a move Clinton “warmly” welcomed in her statement on Friday.

Burma hopes the amnesty and the peace deal will help improve relations with the international community. The United States and European Union have repeatedly called for Burma's nominally civilian government to free all of its political prisoners. After Friday's release, it is unclear how many prisoners of conscience remain in Burmese jails.

Meanwhile, a leading congressional voice behind U.S. sanctions on Burma, Senator Mitch McConnell, says he will begin a three-day visit to the country on Sunday to assess political reforms. He plans to meet pro-democracy activist Aung San Suu Kyi and government officials in his first ever trip to Burma.

Another U.S. congressman, Representative Joe Crowley, is currently in Burma to encourage the government's reform efforts.

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“You're talking about quite a comprehensive list of prominent political activists, journalists, labor activists, Buddhist monks and former members of the government. So this is really quite a significant release.”

“We're actually entering a very interesting phase in modern Burmese politics, and everyone released today certainly has a very prominent role to play in that.”

“This is a momentous day for the diverse people of Burma, and we will continue to support them and their efforts and to encourage the government to take bold steps that build the kind of free and prosperous nation that I heard from everyone I met with they desire to see. We believe that future is achievable.” 19:35 ))