The first U.S ambassador to Myanmar in 22 year formally assumed his job Wednesday by presenting his credentials to the country's president.

Derek Mitchell carried out the formality at the presidential mansion in the capital Naypyitaw, said the website of the office of President Thein Sein. Mitchell had arrived earlier Wednesday in Yangon, Myanmar's biggest city, before proceeding to the capital.

Mitchell previously was President Barack Obama's special envoy to Myanmar. The U.S. Senate confirmed his appointment as ambassador in late June.

Washington announced in January it was restoring full diplomatic relations with Myanmar, encouraged by reforms that have swept the nation since a long-ruling army junta ceded power last year.

Thein Sein, who took office after a general election, has instituted liberal reforms after almost five decades of repressive military rule. The initiative in large part is meant to attract foreign aid and investment.