The search is on for the wreckage of the suspected Pakistani terror boat which blew itself up following a chase and surveillance has been increased along Gujarat coast, security officials said.
Pakistan however rejected India's claim and said no boat from Karachi had gone to the open sea.
The dramatic incident -- a reminder of the manner Pakistani terrorists sneaked into Mumbai in 2008 -- took place on Dec 31-Jan 1 night.
According to Indian defence ministry, the suspicious boat was intercepted by the Coast Guard based on an intelligence input Dec 31, and it was traced in the Arabian Sea, nearly 365 km off Porbandar of Gujarat.
When the boat was approached by a Coast Guard ship, it switched off its light, and tried to escape. Following nearly an hour long chase, the Coast Guard warned the boat to stop for a check.
Four occupants seen onboard then went to a lower deck and set the boat afire. This led to an explosion early morning Jan 1, raising the suspicion of explosives being onboard.
While the defence ministry in a statement Friday had said the boat was "planning some illicit transaction in Arabian Sea", Defence Minister Manohar Parrikar in a comment on his official Facebook page called it a "boat carrying suspected terror groups".
Coast Guard officials said that ships and aircraft are continuing the search operation to recover wreckage or bodies of those who were seen on the boat.
However, an official said that with the sea being atleast 2,000 metres deep in the area, the task is not an easy one.
Talking to reporters in Gandhinagar, Coast Guard Commander (North-West Region) Kuldip Singh Sheoran also said surveillance has been increased.
"We are alert round-the-clock, but due to these events we are on extra alert. Our ships and aircraft are doing their job of patrolling the sea," he told reporters.
He said those onboard did not look like fishermen.
"We saw four men on the boat... they were nowhere looking like fishermen, they were wearing t-shirts and half-pants, and this raised suspicion on our side," Sheoran said.
Asked if the men seen on the boat were terrorists, he said: "Multiple Indian intelligence agencies are jointly investigating the incident and they will go to the bottom to it."
As the incident brought back the memory of the 26/11 attacks, when 10 Pakistani terrorists entered India through Arabian sea and created a 60-hour mayhem in Mumbai during the Nov 26-29, 2008, Home Minister Rajnath Singh India has taken all necessary steps to strengthen security to ensure such incident is not repeated.
"We have strengthened our security on all fronts," he said, adding that security arrangements would be in place as usual for the Republic Day where US President Barack Obama will be the chief guest in Delhi.
Pakistan Foreign Office spokesperson Tasneem Aslam however said no boat from Keti Bunder port of the country's Sindh province had sailed off in the open sea.
Sources in the foreign office termed the Indian claim as mere propaganda to tarnish the image of Pakistan, Geo News reported Saturday.
Gujarat Congress leader Shaktisinh Gohil meanwhile said it would have been better if at least one of the occupants of the "terror" boat had been captured alive.
"We had caught a 26/11 terrorist ( jmal Kasab) alive during the operation. It would have been better if at least one of the boat occupants had been caught alive... India then could have told the world their handlers belonged to Pakistan," Gohil said.