U.S. President Barack Obama said on Friday that Myanmar's decision to release political prisoners is a "substantial step" forward for its democratic reform, according to a White House statement.

"(Myanmar's) President Thein Sein's decision to release hundreds of prisoners of conscience is a substantial step forward for democratic reform," Obama said in the statement.

He said that during her recent visit to Myanmar, U.S. State Secretary Hillary Clinton discussed with the country's leaders steps that would "advance a new beginning between our countries."

"A key part of that discussion was the need to unconditionally release prisoners of conscience and allow them to participate fully in public and political life," said Obama.

He applauded Thein Sein's decision to release hundreds of prisoners of conscience, urging Myanmar's government to ensure all political prisoners are allowed to "participate fully and freely in the political process, particularly the upcoming by-elections."

In accordance with President U Thein Sein's Thursday amnesty order, Myanmar on Friday started to release 651 more prisoners, including a lot of key political prisoners.

Relations between the United States and Myanmar have showed signs of improvement recently. Clinton became the first U.S. secretary of state to visit Myanmar in more than 50 years, as the Obama administration said it saw "flickers of progress" in the Southeast Asian nation.

The U.S. government on Thursday welcomed a peace deal reached between Myanmar's government and Kayin National Union (KNU), the largest anti-government ethnic armed group in the country.