Guwahati, July 14 :     Passengers of an Assam-bound Bhutan bus had a narrow escape when a bomb ripped through it in the Bhutanese border town of Sandrup Jhonkar last night, intelligence sources said here today. The passengers had disembarked for dinner at a roadside hotel at 10 pm. No one was injured. The bus was travelling to Darranga in Lower Assam?s Nalbari district. While the bus was reduced to a ?lump of metal?, a portion of the hotel was also damaged. The bus was parked at the hotel?s parking lot. The sources suspected that the blast might have been triggered by a remote control device ?essentially to spread panic in the area?. The sources refused to comment on the motive behind the explosion but added that most of the passengers were of Bhutanese origin. The bus belonged to the Bhutan Barma Travels. Asked whether any militant outfit from Assam, whose members are camping in Bhutan could be involved, a source said, ?The occupants of the bus were mostly from Bhutan. We don?t see any reason why any extremist outfit should train its gun on its hosts.? The Bhutan government has reportedly served ?quit notices? on the top leadership of the Ulfa pointing out that the presence of their cadres was affecting the peace and tranquillity of the country. There have been reports that following the ?quit notices?, the Ulfa was contemplating migrating to Myanmar. Ulfa leaders held: Three top Ulfa rebels, including a woman activist, were arrested by the BSF in Lower Assam?s Bongaigaon district during the past 48 hours. Deputy commandant of the BSF?s 109 battalion Narendra Singh said a woman leader, Nomali Sutradhar, who was functioning as the outfit?s chief instructor at a training camp inside Bhutan, was arrested on Monday near Bijni in Bongaigaon district. Singh said Sutradhar was imparting lessons on motivation, aims and objectives to the newly-recruited cadres at the Bhutan camp and had sneaked into the state 10 days ago for treatment. The same day, BSF personnel of the same unit apprehended a member of Ulfa?s communications wing of Birjhora Anchalik Parishad, Kandorpo Medhi, from the Abhayapuri market. In another incident yesterday, a mobile check post of the BSF arrested Chandan Baruah, chief of communications wing of the Sankosh Anchalik Parishad from Jogighopa. The BSF personnel recovered several incriminating documents relating to the Ulfa?s central committee from him. The arrested militant leader, a resident of Kokrajhar, said during interrogation that the Ulfa was planning major strikes against the security forces in August-September, sources said.