The United Nations on Sunday condemned a government crackdown in Gambia that it said had led to the death of three opposition party members who were arrested during protests on Thursday.
In a statement echoed by the US state department, UN Secretary General Ban Ki-moon expressed "dismay" at reports that a leading member of the United Democratic Party (UDP), Solo Sandeng, and two other party members had died while in custody.
Government officials were not immediately reachable for comment.
The three opposition party members were held after a small demonstration near the capital Banjul on Thursday in which they demanded electoral reform and protection of free speech in the tiny West African country.
The clampdown continued on Saturday when security forces arrested senior opposition members including the head of the UDP Ousainu Darboe, whose home was raided by police.
The identities of the two other party members were not released and their deaths could not be immediately verified by Reuters, though the UDP said in a statement on Sunday that three of its members had been killed.
Amnesty International had said on Saturday that one detained UDP member, Fatoumata Jawara, was believed to be suffering from serious injuries.
Ban Ki-moon called for a "prompt, thorough and independent investigation into the circumstances that led to their death while under state custody". US state department spokesman John Kirby called on the Gambian government to "uphold its international obligations ... including the right to peaceful assembly."
The statements are likely to put pressure on President Yahya Jammeh, who was in Turkey this week attending a summit of Islamic countries. He is expected to return on Sunday.
Jammeh, who seized power in a bloodless coup in 1994, has made headlines for his eccentric proclamations, including a claim to have invented a cure for HIV/AIDS, and his recent surprise decision to make Gambia an Islamic republic.