New Delhi/Srinagar, March 30: A low-flying chopper, gun-toting escorts in front and behind and police every few hundred metres ? security experts thought they had come up with the most foolproof plan for the April 7 peace bus from Srinagar to Muzaffarabad.

That is till early this afternoon when a fax landed up at news agencies in Srinagar.

The message was from four outfits, believed to be fronts of major militant groups like the Hizb-ul Mujahideen. It warned that Kashmiris who board the bus to the capital of Pakistan-occupied Kashmir would be branded as ?traitors? and threatened to kill them.

?We humbly request the persons selected to travel on first and second bus to Muzaffarabad not to enter the coffin (bus) but if they do, they will find their names in the list of traitors,? said the joint statement from Al-Nasireen, Save Kashmir Movement, Farzandan-e-Millat and Al-Arifeen.

?We are still checking if this is a hoax,? said a senior police officer.

But a chill must have run down the spine of those set for the historic ride. The message came with a list of the passengers along with their addresses, though the names had till then not been made public.

The statement threatened to attack the bus, saying it was being rolled out to keep ?Kashmir with India forever?. It was critical of the Pervez Musharraf regime in Pakistan for ?implementing the Indian agenda on Kashmir under pressure from imperialist forces?.

In Delhi, Union home minister Shivraj Patil said ?fullest precautions? would be taken to ensure that the service runs smoothly.