Naval boats battled rebels on Lake Tanganyika in the east of Democratic Republic of Congo on Thursday as heavy fighting spread close to the lakeside city of Uvira, sources in the area said.
Fighting between the Mai-Mai Yakutumba militia and Congo government forces broke out at the weekend on the outskirts of Uvira, close to the Burundi border. Unrest has mounted since President Joseph Kabila refused to step down when his mandate expired last December.
"Since 0300 GMT there has been an exchange of gunfire between the army and the Mai-Mai in Uvira," said Lubungula Dem's M'Sato, a member of a peacebuilding advocacy group in Uvira, the second largest city in South Kivu province.
Congo's navy also repelled an attack by Mai-Mai rebels in boats on the lake, military spokesman Louis-Claude Tshimwanga said, adding that government ships had sunk one of the rebel's boats and that government forces remained in control of Uvira.
Lake Tanganyika is hundreds of kilometres long and also borders Burundi, Tanzania and Zambia.
"The rebels tried to attack (the city) from the lake. They have motorised pirogues," said a witness in Uvira, who asked not to be named, adding that he saw six rebel boats. "The (navy) caught one but the others escaped."
The Mai-Mai Yakutumba, formed in 2007 by local militiamen opposed to integration in Congo's national army, has well-established gold smuggling networks on the lake.
In an audio statement this week that was shared on social media, its leader William Yakutumba said his forces were rebelling against Kabila's mismanagement of the country's natural resources and failure to quit power when his constitutional mandate expired.
Congo's mineral-rich eastern borderlands are a tinderbox of ethnic tensions and for more than two decades have been racked by violence, often spilling across the country's borders. The region is the world's biggest source of coltan, used in mobile phones and other electronic products.
Congo's UN peacekeeping mission, MONUSCO, said it had deployed troops around Uvira on Wednesday to protect civilians and that the deputy commander of its forces was on the ground to supervise the situation.
"I urge the armed groups to immediately cease this hostility including all forms of violence against constituted authority and innocent civilians," mission head Maman Sidikou said in a statement.