A prominent Egyptian opposition leader was detained on Tuesday for "offending public decency" amid what rights lawyers say is a wave of arrests of potential presidential candidates one year before an election.

Khaled Ali, a human rights lawyer who ran in Egypt's 2012 presidential vote, was questioned by the prosecution and ordered detained for 24 hours pending investigations, lawyer Gamal Eid told Ahram Online.

Ali, who has suggested he might run against President Abdel Fattah el-Sisi in an election slated for 2018, was the main lawyer to bring a case against the government after it agreed to hand over two Red Sea islands to Saudi Arabia in April last year.

The agreement to transfer the islands of Tiran and Sanafir sparked rare protests in Egypt, which bans all but court-approved demonstrations.

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Ali is being sued by a private citizen over a photograph in which he appears to make an "obscene hand gesture" while being lifted up by a crowd following his victory in the aforementioned case, according to his lawyer.

Ali denies the authenticity of the photo.

His detention order follows a spate of recent arrests that rights lawyers say has been directed at opposition figures in Egypt who have indicated they could run against Sisi next year.

Eight members of Ali's left-wing Bread and Freedom Party (BFP) have been detained since April on charges including "misusing social media to incite against the state" and "insulting the president", according to the party's legal adviser.

Egypt's interior ministry denies the arrests are politically motivated.

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Sisi overthrew democratically elected President Mohammed Morsi, of the Muslim Brotherhood, in mid-2013 following street protests against his rule.

He has since launched a persistent and extensive crackdown and has declared the Muslim Brotherhood a "terrorist organisation".

He went on to win a presidential vote in 2014, but has not said whether he will seek re-election when his current term ends in 2018.