"They were aided by the British secret service, that is MI6, .... American Central Intelligence Agency and the Spanish secret service," Zimbabwe's Home Affairs Minister Kembo Mohadi told a news conference on Wednesday, reading from a prepared statement.
He said the heads of the police and army in the tiny but oil-rich central African nation of Equatorial Guinea had gone along with the plot against the government of President Teodoro Obiang Nguema Mbasogo.
The "mercenaries" were held on Monday in Harare.
"The Western intelligence services persuaded Equatorial Guinea's service chiefs not to put up any resistance, but to cooperate with the coup plotters," Mohadi said.
He said the heads of the two services had been promised posts in the post-coup cabinet as a reward.
Zimbabwean authorities had got the information from Simon Mann, who was detained in Zimbabwe on Sunday as he waited to meet a plane carrying 64 men who were detained as suspected mercenaries, he added.
Mohadi said on Tuesday Mann was a former member of Britain's elite commando Special Air Service (SAS).
Zimbabwe's top diplomat to South Africa said on Wednesday the suspected mercenaries could face the death penalty.