The US envoy to Zambia Daniel Foote on Monday warned of "decaying" bilateral ties following a 15-year jail sentence slapped on two men for homosexuality.
Foote recently came under fire after he expressed horror over the high court ruling late last month and urged Lusaka to review laws that discriminate against minority groups.
Zambian Foreign Minister Joseph Malanji reacted immediately, saying he would write a protest letter to Washington that Foote's comments were "tantamount to questioning the Zambian constitution."
Foote told a news conference on Monday that Zambia, which relies on overseas aid, wanted diplomats "with open pocketbooks and closed mouths.
"Let us stop the facade that our governments enjoy warm and cordial relations," he said.
Homosexuality is outlawed in the southern African country which also faces a high HIV burden.
Over the last 15 years, the US has provided more than $4 billion (3.6 billion euros) to fight HIV/Aids in Zambia.
Foote said he would not attend this week's annual Aids day event following "threats" via social media over his comments on the sentencing.
"Your citizens are terrified of being outed as HIV-positive because of the inaccurate and archaic associations between HIV and homosexuality.
"I hope the government of Zambia commits to improve its decaying relationship with the United States but that is a decision for it to make," Foote said.
Zambia is one of the largest per-capita recipients of US assistance in the world, at $500 million each year.
UNAIDS data shows 1.2 million Zambians were living with HIV in 2018 and over 58 percent of which were women.