A new estimate for the amount of money that Zambia owes Chinese lenders is nearly double what the Zambian government had previously admitted.
Zambia spends at least 30% of its income on interest payments, according to credit ratings firm S&P Global.
Last year, it missed an interest repayment, making it the first African country to default on a loan during the pandemic.
The country is now under a new President, Hakainde Hichilema, who told the BBC earlier this month that he had inherited an "empty" treasury.
He said the debt situation had not been "fully disclosed" by the former government.
This included what was owed to Chinese lenders.
A new paper from the China Africa Research Initiative, based at Johns Hopkins University in the US, estimates that the sum now amounts to $6.6bn (£4.8bn). A previous Zambian government figure put it at $3.4bn, the paper’s authors say.
Zambia's finance ministry said these figures were "broadly consistent" with official government reporting, Reuters news agency reports.
It also quotes Bwalya Ngandu, who was finance minister under the former government, as saying: "We have never hidden any debt.”
