William Hague is visiting Burma, the first British Foreign Secretary to do so for more than 50 years.
He is expected to use meetings with the country's leaders to press for the release of more political prisoners.
Last year the Burmese president Thein Sein unexpectedly embarked on a series of liberalising measures, including opening talks with the opposition leader Aung San Suu Kyi.
But critics doubt how genuine moves to democracy are.
Speaking ahead of his arrival in the capital, Naypyitaw, Mr Hague welcomed the "encouraging" steps taken by the government and urged it to do more after years of hardline military rule.
"I am visiting the country to encourage the Burmese government to continue on its path of reform, and to gauge what more Britain can do to support this process," he said.
"Further steps are needed that will have a lasting impact on human rights and political freedom in Burma.
"In particular, we hope to see the release of all remaining political prisoners, free and fair by-elections, humanitarian access to people in conflict areas, and credible steps towards national reconciliation."
Democracy campaigners claim between 590 and 1,700 political prisoners remain behind bars, despite government promises to free them, while reports of abuses against ethnic minorities continue.
Aung San Suu Kyi's National League for Democracy has now re-registered as a political party and will contest a series of 48 parliamentary by-elections due to take place on April 1, in what is being seen as an important test of the reform process.
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