In Zambia, Washington has reportedly mounted pressure on the government to grant access to its critical minerals in exchange for medical care

The US has negotiated 28 international health agreements, most of them with African countries, while refusing to disclose their full terms, triggering a widespread backlash, the Washington Post reported on Monday.

The pacts are part of an "America First" overhaul of foreign health assistance, led by the State Department following the dismantling of the US Agency for International Development last year. The report cited State Department figures saying signed agreements under the new model so far cover $12.7 billion in US assistance and require partner countries to invest $7.8 billion.

Deals involving Kenya, Uganda, Mozambique, Nigeria, and Ethiopia were published online in March before allegedly being removed. Washington later stated that the documents were posted in error and would be republished once all negotiations were concluded.

WaPo said the "secrecy" surrounding the arrangements has sparked concern among partner governments and transparency advocates, who fear that the US is using health assistance to gain concessions on unrelated policy issues.

In Zambia, a deal had been expected in December, but talks reportedly led to "political pressure" amid claims that Washington was attempting to use the health package as leverage in separate negotiations over critical minerals to challenge China's dominance in the sector.

Last month, the New York Times reported that the Trump administration was considering withholding life-saving aid to Zambia's 1.3 million people who rely on daily HIV/AIDS treatment as a "negotiating tactic to force" the southern African country to sign the minerals deal.

Nick Checker, a senior US State Department official for Africa, has denied the allegations, stating that Washington is "not seeking anything at Zambia's expense or against Zambia's laws or interests."

"But, how we negotiate this and what we expect from them will be fundamentally different from approaches of the past that failed to deliver for either Zambia's sustainable future or for the American people," Checker said at a summit in Washington last month, WaPo reported.

READ MORE: Zimbabwe backs out of 'lopsided' US health deal

In February, Zimbabwe rejected a proposed $367 million US health funding agreement as "lopsided," adding that the arrangement failed the test of "mutual respect, transparency, and reciprocal benefit."

Kenya's High Court temporarily suspended a landmark five-year health cooperation deal with the US worth more than $1.6 billion in December, citing concerns that the program could expose the sensitive medical information of Kenyan citizens to unlawful access.

READ MORE: Kenya court suspends 'landmark' US health deal

Peter Maybarduk, director of the government watchdog Public Citizen, which has filed a lawsuit seeking access to some of the agreements secured by the Trump administration, has said disclosure is required to understand what Washington "expects, or extracts, in return." He also accused Washington of treating negotiating partners as "hostiles" and employing a "divide and conquer" approach.