They said it was part of efforts to disrupt the southern Sudan independence referendum due in January.
The former rebel Sudan People's Liberation Army, which controls Southern Sudan under the 2005 peace agreement, said the Sudanese army helicopter gunship attacked SPLA positions in northern Bahr al-Ghazal state.
This comes as a senior official of President Omar al-Beshir's ruling National Congress Party accused the Southern army of aiding Darfur rebels, which he said amounted to a tacit declaration of war.
"We should not be surprised," says John Duku, a former SPLM representative who now heads the Countdown to Southern Southern Referendum. "That's always what the government says. Peace in Darfur is not the private domain of the National Congress Party. We are all Sudanese. The NCP is using Darfur for private political gain."