President Yoweri Museveni vowed renewed pressure against the rebels after their attack on soldiers near Gulu, the BBC reported.
In 18 years of fighting the LRA has displaced 1.5 million Ugandans and abducted more than 20,000 children, turning them into slaves or soldiers, or selling them as slaves to Sudanese buyers.
A limited ceasefire had been declared in November so rebels could discuss peace prospects, but Friday mediators said the insurgents pulled out of a planned peace deal at the last minute because they needed more time to study the document.
Then the attack came.
"It is the rebels who refused to sign the cease-fire memorandum of understanding and this is the reason why the government has taken the decision to start fighting them while the peace option remains," Museveni told Gulu residents.