Rising anti-India anger on websites linked to the LTTE is causing concern in New Delhi, which has alerted Tamil Nadu and other Indian states to increase vigilance against a terror threat from the group.

It may also put a crimp in the campaign outings of Prime Minister Manmohan Singh, Congress party chief Sonia Gandhi, and her son and political heir, Rahul Gandhi, Straits Times website reported.

“The Tamil Nadu coast is vulnerable. We have sensitised the Tamil Nadu government,” Home Minister P. Chidambaram said over the weekend. “The state government is fully alive to the threats.”

Airfields, a nuclear power plant on the Tamil Nadu coast and other key installations have been placed under higher levels of security as New Delhi plays a balancing act with Colombo over the Tamil question.

“We are for fighting terrorists and all sorts of terrorism. Therefore, we have no sympathy for any organisation indulging in terrorist activity, particularly the LTTE, which is a banned organisation in India,” Foreign Minister Pranab Mukherjee said last week, ahead of a visit to Colombo.

According to the report New Delhi's worst fear is a suicide attack from the air on the Kalpakkam nuclear plant outside Chennai.

While Sri Lankan troops have stumbled on LTTE airfields and even an abandoned submersible craft, there has been no trace of the five Czech-built light aircraft.

"There is fear the LTTE may have dismantled the planes and ferried them into Tamil Nadu. While the LTTE have nothing to gain by taking on India directly at a time when they face heavy losses, New Delhi is wary they may be forced to do a favour for other terror groups like Lashkar-i-Taiba, which has repeatedly targeted India," said the website.