GUWAHATI, January 23: The unlawful activities (prevention) tribunal has asked the United Liberation Front of Asom and the National Democratic Front of Boroland to explain why they should not be declared "unlawful associations" by the Centre. In two separate notifications issued yesterday, the tribunal asked both the rebel groups to show cause as to why the Centre's declaration should not be confirmed by the tribunal. The Centre had referred the notifications to two separate tribunals of Justice Cyriac Joseph and Justice Manmohan Sarin of Delhi High Court for adjudicating whether or not there was sufficient cause for declaring the ULFA and the NDFB "unlawful". These notifications are issued every time the ban is extended to a militant outfit. However, none of the outfits have ever responded to these notifications to defend themselves, official sources said. Both the rebel groups have been asked to send their reply to the office of the registrar at Delhi High Court within a month's time. The Centre had issued the notifications on November 27, declaring both the outfits as "unlawful associations", following a spurt in killings and other forms of violence perpetrated by the two militant outfits in the state. As many as 109 Hindi-speaking Assamese people and 13 Bhutan nationals have been killed in 27 incidents of violence perpetrated by the ULFA, the NDFB and the United Peoples' Democratic Solidarity (UPDS) in Nalbari, Tinsukia, Dibrugarh, Sivasagar, Barpeta, Karbi Anglong and Kokrajhar districts since April last year. The figure of civilians killed by militants in the state reached an all-time high last year since the unified command structure became operational in the state in 1997. As many as 412 civilians were killed by militant outfits last year as against 179 civilians killed in 1999. The Assam Police claim that the three main militant outfits in the state - the ULFA, the NDFB and the UPDS - have mostly hit soft targets to prove their existence and terrorise people, out of sheer frustration. This resulted in a spurt in killing of civilians last year. However, unlike the ULFA and the NDFB, the UPDS has not been declared as "unlawful association" by the Centre.