Japhet Chataba and Steven Samba were sentenced on Wednesday to 15 years in prison by the High Court in the capital, Lusaka, after they sought a review of their conviction handed last year by a magistrate's court.

US Ambassador Daniel Foote reacted to the sentence by saying he “was personally horrified to read about the sentencing of two men, who had a consensual relationship, which hurt absolutely no-one”.

Mr Malanji told journalists over the weekend that he will dispatch the protest letter on Monday.

“To question (the judiciary's) decision by a representative of a foreign government is tantamount to questioning the Zambian constitution,” Mr Malanji said.

“Until the Zambian constitution is changed to accommodate that, the courts will always rule according to the Zambian constitution,” he said.

Homosexuality is illegal in Zambia.

Zambia’s President Edgar Lungu has previously warned western countries that the country will not be forced to accept gay rights.