More than 600 people have been killed since rebels began an uprising in two Sudanese states last year, the interior minister said on Tuesday, but an analyst called the figure meaningless.

Ibrahim Mahmoud Hamed, giving a rare casualty count, said in a report to parliament that 296 people were killed in South Kordofan last year after fighting with rebels of the Sudan People's Liberation Movement-North (SPLM-N) began in June.

Another 147 have died this year.

"Most of them are civilians," Hamed said, but he did not specify who killed them.

In Blue Nile state, where the ethnic and religious-minority SPLM-N has been fighting since September 2011, there were 159 fatalities last year and 41 so far in 2012, the minister said.

"There's no way of knowing how many people were killed," Magdi El Gizouli, a fellow at the Rift Valley Institute, told AFP.

"They're not credible," he said of the numbers, partly because the government cannot determine the number of deaths in areas that are not under its control.

Analysts say casualty figures from both sides in the war should be treated with caution.

But the United Nations has reported a steadily increasing number of hungry people fleeing the warzone for South Sudan, where more than 173,000 are now encamped.

Overall, the violence in South Kordofan and Blue Nile has displaced or severely affected hundreds of thousands of people, the UN says.

There have been repeated allegations, denied by Khartoum, that civilians have been bombed from the air.

SPLM-N spokesman Arnu Ngutulu Lodi had no figure for the number of people killed in South Kordofan and Blue Nile but called for an independent international inquiry into the issue.

"Now the rebels in South Kordofan and Blue Nile are targeting civilians," after they "lost their financial source" from South Sudan, Hamed told parliament.

Last week, the rebels launched an unprecedented artillery barrage on the South Kordofan state capital Kadugli, which official media said killed seven women and children.

The UN condemned the attack.

SPLM-N said it regretted any civilian casualties that may have been caused but said its artillery fire was self-defence in the face of government shelling and aerial bombardment of rebel positions.

The action came after Sudan and South Sudan in late September signed deals on security and cooperation that they hailed as ending their countries' conflict.

Among the pacts reached in Addis Ababa is agreement on a demilitarised border buffer zone designed to cut support for SPLM-N in South Kordofan and Blue Nile.

Sudan and South Sudan fought along their undemarcated frontier in March and April, sparking fears of wider war and leading to a UN Security Council resolution ordering a ceasefire and the settlement of unresolved issues, under African Union mediation.

The SPLM-N battled alongside insurgents from southern Sudan who waged a 22-year civil war which ended in a 2005 peace deal leading to South Sudan's independence last July.

Khartoum accuses the government in Juba of backing the insurgents, and South Sudan in turn says Sudan has armed rebels in its territory.