The United Nations peacekeeping chief has condemned a military alliance between rebel movements in Sudan that has the stated goal of overthrowing the government of President Omar al-Bashir.

The head of the United Nations Peacekeeping Operations, Hervé Ladsous, said Tuesday during a briefing to the Security Council that the rebel alliance is counterproductive and could spark further violence.

Last week, various Sudanese rebel groups announced the establishment of the Sudan Revolutionary Front or SRF. The group includes the Sudan People's Liberation Movement-North, which fought for the South during Sudan's north-south civil war.

Sudan has accused South Sudan, which became independent in July, of helping set up the alliance. South Sudan denies the charges.

In his briefing Tuesday, Ladsous also said he was concerned about recent reports of bombings along the border of the two countries.

The U.N. accused Sudan earlier this week of having bombed a refugee camp in South Sudan, a charge which Khartoum denies.

Sudan and South Sudan have been almost constantly at odds since the south became independent in July.

Ladsous urged the two countries to quickly resolve outstanding issues over borders and the sharing of oil revenue during negotiations that are set to resume next week in the Ethiopian capital of Addis Ababa.

On Monday, U.N. Secretary General Ban Ki-moon also expressed “deep concern” over the escalation of rhetoric between the two neighbors.