The first elections since 1990 are scheduled this year, part of the government's so-called "road map to democracy", which critics deride as a sham designed to cement the power of the military which has ruled since 1962.
Calls for dialogue
The country's new electoral laws were widely criticised as designed to keep Aung San Suu Kyi out of the race.
The military government of Myanmar, also known as Burma, has held Aung San Suu Kyi either in prison or under house arrest for 15 of the last 21 years, and she remains under house arrest as she turns 65 on Saturday.
UN's Noeleen Heyzer talks to Al Jazeera about the high cost of Myanmar's isolation
David Cameron, the British prime minister, described the Nobel laureate as "a powerful symbol of the strength of the human spirit".
"The injustice of your continuing detention mirrors the injustice that the regime has inflicted on your country and your people for so many years.
"Throughout that time, you have stood firm, at enormous personal cost, for the principles of liberty and justice," he said in an open letter to Suu Kyi.
Barack Obama also called for her release on Friday.
"I once again call on the Burmese government to release Aung San Suu Kyi and all political prisoners immediately and unconditionally and to allow them to build a more stable, prosperous Burma that respects the rights of all its citizens," the US president said in statement.
"I encourage all stakeholders in Burma to engage in genuine dialogue towards national reconciliation," he added.
Obama lauded Aung San Suu Kyi's determination, courage and personal sacrifice in working for human rights and democratic change in her country, calling her the "world's only imprisoned Nobel peace laureate".
The opposition leader's National League for Democracy won a landslide election victory in 1990 but the military refused to recognise the win or give up its rule.
Under Obama, the US has pursued a new policy of deeper engagement with Myanmar's generals than the administration of his predecessor, George Bush.
But Kurt Campbell, the leading US diplomat for East Asia and the Pacific, said after a visit to Myanmar in May that Washington was troubled that the generals had not moved on any of the issues standing in the way of better ties.