A senior U.S. diplomat says Washington will move cautiously in any further easing of sanctions against Burma.

Assistant Secretary of State Kurt Campbell told a Congressional hearing Wednesday that the U.S. has ruled out an immediate end to its long-standing sanctions against Burma.

Campbell praised the “significant progress” that Burma's new nominally civilian government made since taking power last year. But he said its recent democratic reforms are “reversible,” and that deplorable human rights conditions still persist in the country.

“Much more work needs to be done, including unconditional releases of political prisoners, much more work in advancing civil society, the legislative and legal frameworks of a free and open society.”

Campbell was attempting to reassure U.S. lawmakers, some of whom are concerned that Washington's recently announced relaxing of sanctions may be undermining further democratic reform in Burma.

The United States eased an investment ban, some travel restrictions, and other sanctions in early April after Burma held by-elections in which pro-democracy leader Aung San Suu Kyi's political party won 43 of the 44 seats it contested.

But Campbell said he does not view Burma's reforms with “rose-colored glasses,” and warned the U.S. may reconsider its sanctions policy if the reforms do not continue.

“We recognize very clearly that there have to be provisions and capabilities to be able to respond if there is a reversal or stalling out (of reforms), that leverage is an essential component of our strategy.”

Wednesday's hearing took place as a group of influential human rights organizations, including Human Rights Watch and seven other U.S.-based groups, questioned Washington's sanctions strategy.

The group said any further easing of the sanctions should come only after additional political reforms, including the release of more political prisoners, an end to conflicts with ethnic rebel groups and amendments to Burma's military-drafted constitution.