The government on Friday published a transcript of what it said was opposition leaders plotting a coup.
Oi-Talbek Osmonov, chief of the government security service in Bishkek, said on Saturday: "As far as I know, a criminal case has been opened by the general prosecutor against those on the recording.
"It refers to an attempted violent seizure of power."
Protesters in the impoverished central Asian nation have camped out in a central square demanding the resignation of Kurmanbek Bakiyev, the president.
Although their numbers have dwindled, the country's record of instability has raised fears of unrest.
The demonstrators, who numbered about 1,000 early on Saturday, say Bakiyev is failing to alleviate poverty in the former Soviet state, and is ditching democratic reforms and reneging on a promise to share power with parliament.
Omurbek Tekebayev, a former parliament speaker and one of the opposition movement's leaders, said that compromise could still defuse tensions.
"Our plans are open and transparent. We have no criminal intent," he said.
"There were words on the transcript that were never said, words like coup and revolution."
"Our plans are open and transparent. We have no criminal intent"
opposition movement leader
But, he added, the opposition was still willing to compromise with Bakiyev if constitutional changes that he is due to bring before parliament on Monday offer the elected chamber more power, as it has been demanding.
"We are impatient to see his bill. If it is consensual, that could make a big difference to the situation in the country and opens a new possibility for negotiations."
The protests in the capital, Bishkek, the latest in a months-long row between the opposition and Bakiyev, started on Thursday and attracted about 15,000 people.
Despite the political tensions, daily life in Bishkek has returned to normal with shops that closed on Thursday re-opening for business.