(Adds Ugandan comment)
By Lesley Wroughton
WASHINGTON, June 19 (Reuters) - The United States is set to announce additional measures against Uganda in response to a law that imposes harsh penalties for homosexuality, senior administration officials said on Thursday.
The White House announcement, expected later in the day, will ratchet up punishment on those implementing the law, which was signed by President Yoweri Museveni in February, officials told Reuters.
In Kampala, a government official said the United States had not notified Uganda of additional steps but would not alter its decision to toughen laws against homosexuals.
"Uganda is a sovereign country and can never bow to anybody or be blackmailed by anybody on a decision it took in its interests, even if it involves threats to cut off all financial assistance," government spokesman Ofwono Opondo told Reuters.
President Barack Obama warned Museveni when he signed the law that it would complicate relations between the two countries. Since then, the United States has been reviewing its funding to Uganda, while privately pressing Museveni's government to repeal the law.
Ugandan Foreign Minister Sam Kutesa was in Washington last week meeting with U.S. Secretary of State John Kerry to discuss American concerns about the law, which imposes life imprisonment for those engaging in homosexual sex.
Washington has been careful in its retaliation not to divert funding from projects that will directly affect HIV/AIDS or nutritional programs that benefit ordinary Ugandans.
Uganda is also a key Western ally in the fight against Islamic extremism in Somalia, where Ugandan troops form the backbone of the African Union force battling al Qaeda-aligned militants.
Western donors, including the United States, have already halted or re-directed about $118 million in aid to the East African nation's economy. Steps so far have had limited impact on the budget.
Although aid contributed around 20 percent of the budget this year, it has been falling as a proportion, sliding from 25 percent in 2012-2013 year as Uganda seeks to become less dependent on aid. (Editing by Doina Chiacu and Cynthia Osterman)