An exit poll carried out on behalf of a U.S. government-backed foundation indicates that Kenyan President Mwai Kibaki was defeated in last month's disputed election rather than being re-elected as he claims, according to officials with knowledge of the document.

The head of the International Republican Institute — a nonpartisan democracy-building organization whose work in Kenya was funded by the U.S. Agency for International Development — said the data weren't released because of concerns about their validity.

The institute contracted an experienced Kenyan polling firm, Strategic Public Relations and Research, which had done two previous national-opinion polls for the institute last year. But on election day the institute's staff found that pollsters weren't gathering information in some areas.

Institute President Lorne Craner said institute staffers weren't in all areas where pollsters were working, so they couldn't be sure which areas weren't represented. Officials at the polling firm couldn't be reached for comment, although outside experts said such data problems could be adjusted for statistically.

Craner also said he was wary of releasing the results after protests had begun, but he added that he wouldn't have released them even if there'd been no violence.

"We didn't think it made sense to put out what could be an invalid poll in a climate of great tension," he said.