Two male and two female inmates have been disciplined for having sex at the Idaho Correctional Institution in Orofino, prison officials say.

Meanwhile, the opening of a women's prison in Pocatello that would prevent mixing of the sexes has been delayed from Dec. 1 to as late as February, Corrections Director Richard Vernon said."They had some need to redo things," he said of the project.

Vernon said the sex incident is "a symptom of a women's system that is extremely overcrowded." A record 155 women were in state custody last week, 59 over capacity.

Vernon said the women were on a men's tier because of crowding.

The men picked a lock on a wooden door separating the women from the men's restroom in McKelway Hall, Warden Jim Hope said.

"It was a mutual sexual thing, and they told us how they planned it," he said. "Anytime you house women and men together, you're going to get these things. This was just one they beat us on."

Vernon and Hope declined to announce the names of the inmates and the officer who left the women unsupervised for about 15 minutes on July 29.

An internal review is set for Aug. 24. The inmates could face criminal charges, Deputy Attorney General Bob Gates said. The officer also may be disciplined.

Hope said the inmates admitted violating a rule against sex and are serving 15 days in segregation as punishment.

Three months ago, the American Civil Liberties Union formally opposed the housing of men and women on the same tier. The ACLU is considering suing the state over the issue.

"Had they taken responsible measures, this never would have occurred," said Stephan Pevar, regional counsel for the ACLU in Denver.

"The women should never have been on a male tier. Some women say they're being scared to death."

"That's why we're building a women's prison in Pocatello," Hope said.

Pevar also said the women had warned officers the men were working at picking the locks.

"Despite this second warning, they did nothing," he said. "He (Hope) should be embarrassed that he's operating an institution that has doors separating men and women that can be picked."