CAIRO (Reuters) - Egypt’s state security prosecutor on Thursday remanded for questioning a former Islamist presidential candidate who was detained over alleged contacts with the banned Muslim Brotherhood, state news agency MENA said.

FILE PHOTO: Former presidential candidate Abdel Moneim Abol Fotouh speaks during an interview with Reuters in Cairo February 11, 2014. REUTERS/Asmaa Waguih

Abdel Moneim Abol Fotouh and several leaders of his Strong Egypt party were arrested on Wednesday, a day after he returned from London where he had given interviews critical of President Abdel Fattah al-Sisi.

Sisi is almost guaranteed to win a second term in a presidential election slated for March 26-28, but the vote has been panned by rights groups after a number of potential competitors called off their campaigns, citing intimidation, and a top challenger was arrested.

Abol Fotouh was among several high-profile Egyptians to call last month for a boycott of the election.

The state prosecutor ordered him remanded in custody for 15 days and also instructed him to undergo medical checkups at a prison hospital after “he complained of exhaustion and sudden fatigue”.

The other Strong Egypt party leaders were later released, one of them said.

The Interior Ministry said Abol Fotouh held “secret meetings” with leaders of the international Muslim Brotherhood organization during a visit to London earlier this month to implement a plot to stir unrest and instability in the country.

The ministry said in a statement that authorities had confiscated items, some of which contained instructions to him, including on how to gather crowds on the streets and how to create and inflame a crisis to undermine the state.

One of his lawyers said prosecutors had accused him of holding a leadership post in a “terrorist organization” and publishing false news both inside and outside the country that was likely to harm the national interest. He has not yet been charged.

Abol Fotouh denied the accusations. “All charges are false and malicious,” he said, according to defense lawyer Abdelrahman Haridy.

The 67-year-old physician quit the Muslim Brotherhood in 2011 to mount an independent bid for the presidency in 2012, and has distanced himself from the group since then.

Egypt banned the Brotherhood in 2013 after Islamist President Mohamed Mursi was ousted by the military following mass protests against his rule. The group has since been declared a terrorist organization by the government.

The Brotherhood maintains it seeks political change by peaceful means.

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The Strong Egypt party announced it was suspending activities and said the arrests marked “a complete closure by the ruling regime of political life in Egypt”. The party said it holds Egypt’s government responsible for Abol Fotouh’s safety.

Egypt’s electoral commission has vowed to conduct the vote “according to principles of independence, transparency and objectivity”.

Abol Fotouh was detained days after an interview with Al Jazeera Mubasher, a Qatar-based channel banned in Egypt, in which he criticized what he called the menacing atmosphere of the election campaign.

He also accused Sisi of pulling the army into politics, failing to curb deadly attacks by Islamist militants and mismanaging the economy.

“Any attempt from any president, whether Abdel Fattah al-Sisi or those before or after him, to push the army to be an actor in the political process, I consider this a crime. We will not accept this as Egyptians,” he told Al Jazeera.

He was referring to a stern warning last month from Sisi to anyone looking to challenge his rule.

“The repression in advance of Egypt’s presidential election is a substantial escalation in a political environment that denies people’s rights to political participation and to freedom of expression,” a statement from 14 local and international rights groups said this week.