The U.N. peacekeeping chief on Tuesday condemned an alliance between rebels in Sudan's conflict-torn Darfur region and southern border states, saying it was counterproductive and would spark more violence.

This represents a further step in a pattern of escalation that is counterproductive, Herve Ladsous, head of the Department of Peacekeeping Operations, told the U.N. Security Council.

The United Nations continues to stress that all parties to the different conflicts between the government of Sudan and its peripheries need to return to the table of negotiations and resolve their differences through political dialogue.

Rebels in Sudan's Darfur and the troubled southern states bordering on South Sudan said on Saturday they had formed an alliance to topple the government of President Omar Hassan al-Bashir in Khartoum.

Sudan has accused South Sudan, which split away as an independent country in July, of having helped set up the alliance and called it an act of aggression.

Analysts said the new alliance showed closer coordination among various rebel groups left in Sudan after the South seceded under the terms of a 2005 peace agreement.

Sudan's army is fighting separate insurgencies in the western region of Darfur as well as in the southern states of South Kordofan and Blue Nile bordering South Sudan.

Violence in the joint border region has led to tensions between Khartoum and South Sudan.

The United Nations accused Sudan this week of having bombed a refugee camp in South Sudan, a charge denied by Khartoum. Khartoum and Juba accuse each other of backing rebels in each other's territories.

The north Sudanese government rejected the accusation and said there were no refugee camps in the area, but warned that Khartoum had the right to pursue rebels there.

(Reporting by Louis Charbonneau; Editing by Jackie Frank)