The United States says Zambia failed to engage on a new health aid agreement governing more than $1 billion in US funding, saying repeated outreach from Washington had been ignored as an April 30 deadline passed without a deal.

Outgoing U.S. ambassador Michael Gonzales said the failure to finalise the memorandum of understanding (MOU) had left funding continuing on an ad hoc basis.

Health advocates have warned that the deal links the money to mining access and poses data-sharing risks.

Gonzales rejected what he called "disgusting and patently false" allegations that Washington was threatening to withhold life-saving healthcare support "unless we get critical minerals", in remarks delivered on Thursday as he prepared to leave the post.

‘Open to dialogue’

Zambia's presidential spokesperson Clayson Hamasaka said the government would engage with Washington through diplomatic channels.

"We appreciate the support we have received from the US and other countries...If there are any concerns, we are open to dialogue but that should be done through laid down diplomatic channels," Hamasaka said in response to Gonzales' remarks.

The agreement also requires about $340 million in co-financing from the Zambian government over the same period, according to a draft reviewed by Reuters.

Gonzales said Washington had faced "effectively zero substantive engagement" from Zambian officials since January, with calls going unanswered and meetings cancelled, preventing meaningful negotiations on future cooperation.

Honour commitment

The agreement had been due to be signed in November but stalled after revised drafts were circulated.

Gonzales said the US would continue to honour its long-standing commitment to the Zambian people, including providing antiretroviral drugs and preventing mother-to-child HIV transmission, but warned that large-scale aid would depend on concrete reforms.