The government said last Wednesday it had detained 32 foreigners, mainly South Africans, Nigerians and Americans, for planning a coup before the country's presidential and parliamentary polls on July 30.
Diplomats and security sources said the arrests were about domestic political rivalries and dismissed talk of a plot.
Government spokesman Henri Mova Sakanyi said on Sunday: "We expelled them yesterday. We don't have time to try them ourselves as we are in the middle of organising elections.
"We've discussed the issue with their respective governments and we've sent them to be dealt with by their own countries."
Most of the men were South African employees of a Pretoria-based security firm and had been providing security training for Congo's National Transport Authority.
But some were advisers to Oscar Kashala, a Congolese presidential candidate and Harvard-trained doctor who is one of 32 contenders vying with Joseph Kabila, Congo's president, for the country's top job.
The Congo has been devastated
by five years of conflict
A security source said the men had been released because there was no evidence to back up claims of a coup plot and their detention had drawn sharp criticism from international donors.
Government officials accused the foreign security experts of trying to destabilise the country before its first free national polls in four decades.
But international diplomats accused the government of exploiting the allegations to harass political opponents.
Kashala, a wealthy doctor who has lived in the US, said the arrests were part of a campaign by the government to intimidate him and others and undermine their election chances.
Congo's July 30 polls will be the first multi-party elections in four decades in the former Belgian colony, a nation roughly the size of Western Europe.
They are meant to draw a line under Congo's latest war, which was officially declared over in 2003.
The conflict triggered a humanitarian crisis that has killed four million people since it began in 1998.