COLOMBO, Sri Lanka—One person has been killed and about 15 wounded when Sri Lanka's military shot at protesters demanding clean drinking water, according to television footage and demonstrators.

The shooting happened Thursday evening in Weliweriya, 12 miles (20 kilometers) northeast of the capital, Colombo, when more than 4,000 protesters had gathered to demand action after chemical emissions from a factory had polluted drinking water in about 15 local villages, said one protester, who spoke on condition of anonymity, fearing reprisals.

Residents have been demanding for more than a month that authorities close the factory, the protester said.

He said police used tear gas to break up the protest, but when protesters clashed with police, the army shot at them. He said soldiers shot at some protesters as they tried to flee.

Military spokesman Brig. Ruwan Wanigasooriya said Friday that the army did not aim their guns at the protesters but shot in the air to disperse them. He said "people with other agendas" were behind the protesters and had armed them with firearms and petrol bombs. He did not say who the instigators were or what their motives were.

However, footage from a local television station showed soldiers shooting at running protesters. One scene shows a wounded man being dragged away by another. Another man appears to be hit by a bullet while he tries to rescue a man lying on the ground.

Protesters are shown hurling rocks at the army.

Police spokesman Buddika Siriwardene confirmed that one person had died and 15 were hospitalized but declined to comment on the nature of the injuries.

Siriwardene said the situation arose because protesters blocked a main road, obstructing traffic, despite agreeing with authorities to call off the demonstrations until investigations into the possible chemical leak were complete.

He said the demonstrators struck police with stones and bottles.

Reporters said soldiers beat up several reporters and photographers covering the incident and smashed their cameras.

Kanchana Dissanayake, editor of Sinhala-language "Ada" (Today), said a photographer from the newspaper was admitted to a hospital after being beaten by soldiers.

Human rights activists have accused the Sri Lankan government of reacting sharply to any opposition to its rule since defeating Tamil Tiger rebels in May 2009, ending a nearly three-decade civil war.

The incident is the third in two years in Sri Lanka where police or military have used firearms on protesters. In 2011, a factory worker was shot dead during a demonstration, and in 2012 police shot and killed a fisherman who was protesting against rising fuel prices.