The head of the national opposition Congress party, Rahul Gandhi, condemned the use of lethal force, calling it "a brutal example of state-sponsored terrorism".
The protests against Vedanta's Sterlite Copper plant have been going on in Tuticorin for over three months now, but violence erupted on Tuesday.
Meanwhile, The Sensex and Nifty tanked, dragged by energy stocks such as HPCL and ONGC on rising concern that the government may ask state-owned oil firms to share the burden of higher petrol and diesel prices.
Protesters set vehicles on fire and threw stones at police, Palaniswami said in a statement.More news: Ocado signs USA partnership
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After the Makkal Needhi Maiam chief left, police in riot gear had tried to clear out protesters who'd gathered around the premises. "My thoughts & prayers are with the families of these martyrs and the injured".
Chennai: Bodies of the individuals who were killed in Tuesday's anti-Sterlite protest in Thoothukudi will be preserved until further orders, the Madras High Court said on Wednesday.
In retaliation, police officials resorted to lathi-charge and tear gas to disperse the crowd to contain the situation.
Fresh police firing took place in Anna Nagar, a locality in Tuticorin (also known as Thoothukudi), as public ire showed little sign of abating. About 20 police officers were also injured in the skirmish, which occurred in the southern port city Tuticorin.
Environmental activists say the cooper plant is polluting local water resources, allegations the company denied as "false propaganda". The Politburo demands that plant should be shut down immediately.