CAIRO — A military court on Tuesday sentenced a former government anticorruption czar to five years in prison over incendiary claims about documents said to incriminate Egypt’s leaders, his lawyers and state news media said.

The sentence levied against the official, Hisham Geneina, who had served under President Abdel Fattah el-Sisi until 2016 when he became one of the president’s sharpest critics, signaled that the harsh crackdown on the opposition that preceded last month’s election was set to continue.

Mr. Geneina was one of several opposition figures detained before the vote, effectively clearing the field for Mr. Sisi, who ultimately faced a single token candidate and won with 97 percent of valid votes. All of the opposition figures remain in jail, including Sami Anan, a former army chief whose campaign lasted four days before he was arrested.

Mr. Geneina, a senior figure in Mr. Anan’s campaign, was arrested in March after he said in an interview with HuffPost Arabi that Mr. Anan possessed documents that could incriminate Egypt’s “leadership.” Mr. Geneina said the papers were in safekeeping outside Egypt, but he did not specify what they were.