Senegalese police have released four people detained last week over an alleged plot to overthrow the regime of President Abdoulaye Wade, a security services official said Tuesday.

They "were freed yesterday [Monday] evening. For the charges, we are waiting for more clarity. We have not yet closed the inquiry," the source said.

The four, described by an official on Monday as "youths, including ordinary citizens and opposition activists," were arrested on Friday last week.

The Senegalese government said over the weekend that it was investigating an alleged coup plot, with the announcement coming against a background of demonstrations, but the opposition has derided the claims of such a plan.

Justice Minister Cheikh Tidiane Sy referred in a weekend statement about the alleged plot to an opposition coalition called Benno Siggil Senegal, or Together for the Renewal of Senegal.

A heated debate has been under way since Wade, 85, announced last September that he would run for office again. He was elected in March 2000 for seven years, then re-elected in 2005 for five years after an amendment to the constitution.

The opposition argues that 2012 will mark the end of Wade's two mandates under the law, but his ruling Senegalese Democratic Party (PDS) contends that the mandates should be counted from 2007, when the new five-year terms took effect.

Demonstrations were held on Saturday in several towns by Wade supporters, who came to power 11 years ago on 19 March, as well as by the opposition, which wants him to step down.

Rights activist, Alioune Tine, said the claims of a coup were aimed at scare-mongering.

"It is an invention to create fear, a manoeuvre by a power that has lost its head," said Tine, president of the Raddho human rights group based in Dakar.