The Ugandan army on Wednesday also charged that the insurgency was in violation of a truce agreement signed in 2006 to pave the way for peace talks under way in southern Sudan.
The LRA, however, denied responsibility for Monday's attack on the passengers travelling in three lorries from southern Sudan to Uganda.
"Three trucks heading from Sudan to Uganda were ambushed and the occupants abducted. They were moved about one-and-a-half kilometres from the scene as one of the eight victims escaped and the seven were undressed, the rebels tied their hands at their backs and used clubs to smash their heads and kill them," said army spokesman Lt Chris Magezi, quoting an account of the incident obtained from the survivor.
"This is a blatant violation of the [truce] agreement and it is an indication that they [the LRA] lack seriousness to pursue a peace deal with the government. The mediators and observers should investigate these incidents because they are of concern to us," said Magezi.
Justin Labeja, a member of the LRA delegation to the peace talks in Juba, the capital of southern Sudan, said the army's accusation was "unfair", telling IRIN by telephone from Juba: "It is always fashionable for the Ugandan military to blame any attack on the LRA."
The talks resumed on 27 April after four months of uncertainty that followed an LRA demand that Sudanese mediators be replaced and the venue of the talks moved. The United Nations special envoy to the talks, Joaquim Chissano, managed to convince the LRA to abandon its demands and go back to the negotiating table. The cessation of hostilities agreement initially signed in August 2006 has been extended until the end of June and the rebels have six weeks to assemble at Ri-Kwangba in southern Sudan during the talks.
The peace talks are aimed at ending the conflict that has raged in northern Ugandan since 1988, when the elusive LRA leader Joseph Kony took over leadership of a two-year-old rebellion among northern Uganda's ethnic Acholi minority. Thousands of civilians have died in the war and nearly two million people have been displaced by the conflict and forced to live in squalid camps.
Kony and four other LRA leaders have been indicted by the International Criminal Court on charges of war crimes, including the abduction of thousands of children for conscription into the LRA forces and forced marriage to soldiers.