Favouring coordinated patrolling, National Security Adviser M K Narayanan on Tuesday said that the Centre would take all necessary steps including enhancing security to protect Tamil Nadu fishermen from attacks on high seas.

"We will have to start coordinated patrolling," Narayanan told reporters after his meeting with Tamil Nadu Chief Minister M Karunanidhi to discuss issues relating to the kidnapping and attack on fishermen.

Narayanan, however, made it clear that there cannot be joint patrolling between the navies of India and Sri Lanka.

He said security would be enhanced to protect Tamil Nadu fishermen.

To a question whether there was any threat from the Sea Tigers (naval wing of Liberation Tigers of Tamil Eelam), Narayanan said, "Sea Tigers are a threat. Otherwise why should we increase the security."

"LTTE is a terrorist organisation. We are always concerned over any terrorist organisation having sea capability or air capability," he said when asked what type of threat the country faced in the southern coast.

At his meeting with Prime Minister Manmohan Singh on Monday, Karunanidhi drew his attention to the kidnapping and attacks on fishermen from the state on the high seas.

The prime minister had directed the NSA to hold discussions with the chief minister.

Karunanidhi said that Narayanan would visit Chennai on May 31 for a detailed discussion on the issue.

"I told the chief minister that whatever required will be done" to protect the Tamil fishermen, Narayanan said adding, that he explained to the chief minister the steps taken by the Centre to enhance security.

About coordinated patrolling, he said the opinion of Sri Lanka was also required in this regard and "I do not think there is any problem from our side."

To a question whether New Delhi planned to step up assistance to Sri Lankan defence forces to tackle LTTE, he said, "Ask the political leadership."

During his talks with the prime minister on Monday, Karunanidhi had particularly mentioned the recent kidnapping of 12 fishermen and their subsequent release.

"I requested the prime minister to take immediate steps to put an end to such incidents," Karunanidhi had said.