Rebels in Sudan's Blue Nile said on Friday that they had killed 79 government troops and militiamen in two ambushes in the ethnically divided state near the border with South Sudan.
The attacks came on Tuesday and Wednesday in roughly the same area, mountainous terrain about 35 kilometres (20 miles) south of the state capital Ed Damazin, said Arnu Ngutulu Lodi, spokesman for the rebel Sudan People's Liberation Movement-North (SPLM-N).
The group, which was a civil war ally of the former rebels who now rule independent South Sudan, has been fighting for several months in Blue Nile and South Kordofan states, both of which border the South.
Sudan's army spokesman could not immediately be reached.
Lodi, whose forces deny being supported by the South, said there has been an upsurge in fighting in Blue Nile since border clashes between Sudan and South Sudan escalated last week with waves of air strikes hitting the South, and Juba seizing the north's Heglig oil hub on April 10.
Heglig is part of South Kordofan.
Lodi alleged Khartoum is using the Heglig standoff as an opportunity to mobilise militias and other fighters against the SPLM-N. "That's how we see it," he said.
The border fighting between the two neighbouring states has sparked fears of all-out war.