A 24-year-old student who was hit by police gunfire at an environmental protest in western Gambia died on Wednesday, bringing the death toll from the violence to three, his campaign group said."Amadou Nyang, who was shot by Police Intervention Unit personnel during the protest, passed away at the Edward Francis Small Teaching Hospital early Wednesday morning," said Pa Jobe, head of an association calling itself the Faraba Banta Village Development group. Local people have been protesting at Faraba Banta, located about 50km south of the capital Banjul, over the mining of sand which is sold to the construction industry. The activity, they say, is badly polluting rice farms.The violence occurred on Monday. Two other young men were killed, and six civilians and 16 police were injured, according to an official toll.Six protesters were arrested during the demonstration, and Jobe said on Wednesday evening that five of them had been released "unconditionally", adding some had sustained injuries in the clashes.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTER FOLLOW News24 Africa on Twitter and FacebookFive police officers were also detained after the violence.On Tuesday, President Adama Barrow - who last year succeeded the autocrat Yahya Jammeh - said Gambia was in "mourning" and that he had ordered a "full investigation" into the incident."The Gambia has been known for its culture of peace and stability, which makes it the pride of Africa," he said."There is no reason why we should resort to violence or illegal use of force to solve our problems."Human Rights Watch and Amnesty International issued a statement saying that, according to witnesses, demonstrators had been blocking mining-related road traffic when police reinforcements arrived and opened fire without warning.The violence "conjured up painful memories from Gambia's recent past," said Sabrina Mahtani, West Africa researcher at Amnesty, referring to Jammeh's 22-year iron-fisted rule.The two groups called on the government to step up reforms of the police, especially in the areas of training and equipment, to avoid such episodes in the future.