The announcement from LRA supremo Joseph Kony, through his deputy Vincent Otti, came as Kampala said the refusal of the top two rebel leaders to attend the on-again, off-again negotiations would not derail the process.
Mr Otti, who is wanted by the International Criminal Court, rejected a request by mediators to attend the peace talks, saying he feared arrest.
In a statement Mr Otti said Mr Kony had ordered rebel commanders to end all attacks in conflict-ravaged northern Uganda.
The statement was read to news agency AFP by LRA spokesman Obonyo Olweny at the remote town of Nabanga on the border between Sudan and the Democratic Republic of Congo, where the rebel leadership is holed up.
"I, lieutenant general Vincent Otti, on behalf of General Joseph Kony, chairman of the LRA high command, do hereby declare a unilateral cessation of hostilities," Mr Otti said.
"By this statement, I order all our field commanders to, with immediate effect, cease all form of hostilities against Ugandan People's Defence Forces positions and others," he said.
Mr Otti called on the Ugandan government, which has thus far refused to entertain the idea of a truce arguing it should be part of a comprehensive settlement, to issue similar orders to its armed forces.
"I hope the government of Uganda shall reciprocate this gesture of goodwill so that the parties may finally sign a bilateral agreement to provide a peaceful atmosphere for our people while the peace talks continue," he said.
Kampala reacted cautiously to the rebel announcement, which came after the Ugandan delegation said it would return to the peace talks in Juba, the capital of autonomous southern Sudan even though Mr Kony and Mr Otti would not be there.
"There is no problem with what they are saying, but Uganda believes that anything to do with a ceasefire or cessation of hostities should be discussed in Juba," Deputy Foreign Minister Okello Oryem told AFP.
"Let the LRA delegation go to Juba for the talks and relay the same message at the talks," said minister Oryem, also the number two in Uganda's team to the negotiations.
The talks had been thrown into uncertainty on Wednesday when the lead mediator, southern Sudan's vice president Riek Machar, left Nabanga after failing to convince either Mr Kony or Mr Otti to travel to Juba.
The pair rebuffed repeated appeals to participate in the talks, citing their fear of arrest since they, and three other top LRA commanders, have been charged with war crimes by the International Criminal Court in The Hague.
But the chief of Uganda's delegation said in Kampala on Friday that the team would return to Juba despite their absence and in his statement, Mr Otti hinted that he or Mr Kony could attend the talks in due course.
"In the future, we may add or reinforce the delegation, as and when necessary," Mr Otti said.
The talks began on July 14 but were adjourned for consultations after 10 days and started up again on July 31 before a new halt was called Wednesday when a frustrated Mr Machar returned to Juba.
The LRA launched one of the world's most brutal insurrections from northern Uganda 20 years ago, later moving to south Sudan and lately hiding out in the jungles of east Congo.
The cult-like LRA is accused of killing civilians and mutilating victims in a war against the Ugandan government that has uprooted nearly two million people and killed tens of thousands, as well as destabilising southern Sudan.
Mr Kony, a self-proclaimed prophet and mystic who says he speaks directly to God, purports to be fighting to replace Ugandan President Yoweri Museveni's government with one based on the Biblical Ten Commandments.
But the LRA has become better known for atrocities, particularly the kidnapping of an estimated 25,000 children -- girls for sex slaves and boys for fighters.
The United Nations and relief agencies describe the conflict as one of the world's worst humanitarian crises.
Numerous previous attempts to negotiate a peace deal between Museveni's government and the rebels have failed, with each side accusing the other of sabotage.