The party of former rebels in Sudan is calling for the overthrow of Sudanese President Omar al-Bashir.

In an interview Thursday with VOA , Yasir Arman, who heads the Sudan People's Liberation Movement-North, said “it's high time to change the regime in Khartoum.”

Arman said President Bashir is worse than ousted Libyan leader Moammar Gadhafi and ousted Tunisian President Zine El Abadine Ben Ali. He also accused Mr. Bashir's National Congress Party of committing atrocities in the border state of Southern Kordofan, where Sudan's army has been fighting pro-South Sudan forces since June.

This is the first time the SPLM-North has openly called for Mr. Bashir's ouster.

The party is the northern branch of South Sudan's ruling party, which split into two when South Sudan declared independence from Sudan two months ago.

Pro-southern elements are also fighting Sudan's army in Blue Nile state.

A news release from Arman Thursday said pro-southern fighters in the state had beaten back a Sudanese offensive and captured some equipment.

Earlier, the Sudan Armed Forces said it had inflicted “heavy casualties” on the fighters during a clash Wednesday. The army said some soldiers were also killed.

The U.N. has raised concerns about the humanitarian impact of the fighting in Blue Nile and Southern Kordofan, while the United States says the fighting is an obstacle to improving ties with Khartoum.

Sudanese President Bashir is wanted by the International Criminal Court for alleged war crimes, crimes against humanity, and genocide in Sudan's Darfur region. His government has been fighting rebels there since 2003.