Uganda's Lord's Resistance Army (LRA) rebels said on Wednesday they had killed a Ugandan officer in neighbouring southern Sudan, further straining a truce aimed at ending one of Africa's longest conflicts.
Independent monitors say both sides have violated the deal signed in August, but tensions mounted sharply this week as both accused each other of launching attacks in the remote region.
"Ugandan soldiers, as usual, attacked our men," said Godfrey Ayoo, an LRA spokesman at troubled peace talks in south Sudan's capital Juba. "In self-defence we killed their captain and that would not have happened if they has not provoked us."
Ayoo said the clash took place on Tuesday by the River Nile, 115 km (70 miles) south of Juba, as the LRA fighters were walking to an assembly location under the terms of the truce. A Ugandan military spokesman had earlier rejected that, saying the captain was alone when he was shot by the rebels.
"This officer was just walking ... when he was attacked," Major Felix Kulayigye told a news conference. "This is a blatant violation of the cessation of hostilities agreement."
Under the truce, the rebels were meant to gather at two places in south Sudan: Owiny-Ki-Bul, on the Ugandan border and Ri-Kwangba, on the border with Democratic Republic of Congo (DRC), near the LRA leadership's main jungle hideout.
Although around 800 rebels were reported to be at Owiny-Ki-Bul, many fled accusing the army of surrounding them.
MISTRUST
Uganda's military suspects LRA fighters in north Uganda and south Sudan are trying to join the bulk of the rebels in DRC.
"What were they doing at the Nile? They were supposed to be in Owiny-Ki-Bul," Kulayigye said.
"This, plus the clashes at the end of last week between the LRA and local militias, is testament to what we have always said: that the LRA is trying to cross the Nile."
Earlier this week, Uganda's military rejected LRA claims it had ambushed a rebel group in the area, injuring two, saying it had reports the guerrillas fought with local militiamen instead.
A team of independent monitors representing different parties to the conflict set off on Tuesday to probe the claims.
Uganda's 20-year war has killed tens of thousands and uprooted some 2 million more, triggering a humanitarian crisis.
But landmark talks mediated by the southern Sudanese in Juba have been hobbled by profound mistrust between the two sides.
One LRA delegate said Ugandan troops arrested him on Tuesday as he tried to deliver food to Owiny-Ki-Bul. Rei Achama, an LRA major, told Reuters he was freed after four hours.
Monitors said they had received no explanation yet from the Ugandan military, but had filed a report with the mediators.