Mohamed Nasheed, the Indian Ocean nation's first democratically elected president, was arrested a week ago for allegedly ordering the military to detain a Criminal Court chief judge in 2012 and ignoring a Supreme Court order to release him.
Nasheed, who had resigned after weeks of protests and lost the 2013 election, has been charged him under the country's anti-terrorism law.
Eva Abdulla said her Maldivian Democratic Party and another ally decided yesterday that opposition supporters would stage nightly demonstrations until Nasheed is released.
On Friday, thousands of Nasheed's supporters took to the streets of the capital, Male, to demand his freedom.
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Nasheed has denied ordering the arrest of the judge and supporters say the allegation is politically motivated and part of Gayoom's attempt to eliminate potential rivals in the 2018 presidential election.
Nasheed defeated the current president's half brother, Maumoon Abdul Gayoom, in 2008 to end nearly 30 years of autocratic rule.
Although Nasheed, a one-time rights activist, began his term with great hopes, he soon became battered by protests, including by Islamic activists demanding more religiously conservative policies in the Sunni Muslim nation of 300,000 people.