WASHINGTON (AFP) ― President Barack Obama Thursday eased investment curbs on Myanmar and named the first U.S. ambassador to the country in more than 20 years, hoping to reward a “nascent” political reform drive.

But Obama, seeking maximum leverage on Myanmar’s nominally civilian government and to preserve his options in case of “backsliding,” maintained wider U.S. sanctions on Myanmar and figures linked to the former junta.

“As an iron fist has unclenched in Burma, we have extended our hand, and are entering a new phase in our engagement on behalf of a more democratic and prosperous future for the Burmese people,” Obama said in a statement.

Obama’s move followed calls from business and political figures in the United States, Europe and Asia to lift sanctions, and warnings by democracy icon Aung San Suu Kyi against excessive optimism over a political opening.

The U.S. government will now license certain types of investment in financial services and allow U.S. businesses to work in Myanmar, though will ensure that those who abuse human rights and seek to slow progress do not benefit.

“It is a recognition of progress, it is a recognition that opening up greater economic engagement between our two countries is important to support reformers,” a U.S. official said, speaking on condition of anonymity.

Obama also said however that current sanctions law would stay on the books to encourage further reform and to allow a speedy reimposition of tough measures if the United States sensed “backsliding.”

Secretary of State Hillary Clinton, who made a historic trip to Myanmar in December, pressed the authorities to release more political prisoners, after meeting Myanmar Foreign Minister Wunna Maung Lwin.

The U.S. move decision could usher in the first major trade and investment between the United States and Myanmar for years, and help pry open a backward economy left behind by speeding Southeast Asian development.

The U.S. government will maintain restrictions on investment with the military, which has deep commercial interests in the country’s economy.

Obama also nominated Derek Mitchell, who has been serving as the State Department’s special representative to Myanmar, as U.S. ambassador, pending confirmation by the U.S. Senate.

Washington withdrew its ambassador to Myanmar, also known as Burma, after a crackdown on a democracy uprising in 1988 and elections won by Suu Kyi’s democracy movement in 1990 that were never recognized by the junta.

“Burma has made important strides, but the political opening is nascent, and we continue to have concerns, including remaining political prisoners, ongoing conflict, and serious human rights abuses in ethnic areas,” Obama said.

U.S. law currently requires the president to restrict imports from Myanmar, where civilians backed by the military now rule, and bans U.S. investment and export of financial services to the country.

It also blocks property and assets of certain members of the Myanmar ruling class and senior officials linked to the former junta.

A statement from Republican Senate Majority leader Mitch McConnell and his party colleague Senator John McCain pointed to strong bipartisan support for Obama’s approach on Capitol Hill.

“Today’s announcements strike an appropriate balance between encouraging the process of reform now unfolding in Burma, while maintaining sufficient leverage to continue pressing the Burmese government for additional progress,” the two senators said.

They noted the move did not amount to lifting sanctions but was a “conditional suspension” of some measures, and that punishments for those who steal Myanmar’s resources and abuse human rights would remain in place.

The U.S. Campaign for Burma however expressed concern at the U.S. move, saying it sent the wrong message at a time when the Myanmar military was escalating its support against the ethnic Kachin minority in northern Myanmar.

President Thein Sein surprised many U.S. observers by initiating political reforms designed to break Myanmar’s isolation, and elections saw Suu Kyi’s National League for Democracy securing 43 of the 44 seats it contested in parliamentary by-elections.

But it remains a minority, with many seats in both chambers reserved for unelected military officials.

Suu Kyi, sworn in May 2 as a member of parliament after spending most of the past two decades under house arrest, spoke to a gathering of U.S. politicians and rights advocates including ex-president George W. Bush, via Skype this week.

She warned that she felt sometimes that “people are too optimistic about the scene in Burma. You have to remember that the democratization process is not irreversible.”