The United Nations secretary-general has said two more Gambian opposition party members have died in detention following a demonstration Thursday.

The U.N. Secretary-General Ban Ki-moon in a statement Sunday said he was dismayed by the death of United Democratic Party member Solo Sandeng and two fellow party members. He called for an independent investigation into the deaths in state custody. Ban said he was deeply concerned about the apparent use of excessive force and called on authorities to unconditionally release others arrested.

The U.N. said party leader Ousainou Darboe has also been arrested.

Gambian opposition party members and others staged peaceful protests in Serrekunda calling for electoral reforms before the December 2016 presidential elections.

Rights group say President Yahya Jammeh's rule since 1994 has been marred by human rights violations.