Anti-nuclear activists today held a day-long siege of Kudankulam atomic power plant from the sea with the protesters anchoring more than 800 boats in their fourth phase of agitation against the project.

Fishermen, spearheaded by the People's Movement Against Nuclear Energy (PMANE), positioned fibre boats and floating buoys in the sea about 500 m from the plant, about 70 km from here, insisting on their demand for scrapping the Indo-Russian project.

The fishermen from Tirunelveli, Kanyakumari and Tuticorin took part in the protest as over 5,000 security personnel including Rapid Action Force, supported by 10 coastguard boats, kept a close vigil on the situation.

Police said the agitation was peaceful. Barbed wire fences had been put up by police at important places to prevent fishermen from invading the plant.

Additional DGP T K Rajendran supervised the security.

PMANE convenor S P Udhayakumar demanded withdrawal of police from Kudankulam and surrounding villages and "false cases" against anti-nuclear activists besides release of those arrested.

He said fishermen from 48 coastal villages participated in today's "peaceful" agitation.

Udhayakumar also said they would launch their next agitation in Chennai on October 29 when the assembly session begins.

Referring to the arrest warrant issued against him in connection with the protest and violence during the agitation, he said he would face it legally.

This is the second time the protesters are laying a siege from sea after September 22, when they did so at Tuticorin port against loading of uranium in the atomic power plant.

The protesters had last month staged a 'Jal Satyagraha' in the sea at Koothakuzhi, 10 km from Kudankulam, by forming a human chain.

The first unit of the Indo-Russian project was scheduled to be commissioned in December last year but had been delayed due to protests by locals on safety concerns.