"The secretary general is seriously concerned by the major escalation of violence in the Jebel Marra region of Darfur, particularly the heavy fighting in the Golo and Shearia areas that has forced humanitarian agencies to evacuate," Annan's spokesman said in a statement on Friday.
  
Annan, who is currently on a visit to Switzerland, specifically condemned the attack by rebel Sudan Liberation Army (SLA) forces on Golo and called on all parties to immediately stop all hostility, spokesman Stephane Dujarric said.
  
The UN chief reiterated his call on the warring sides to seek a lasting solution to their conflict through negotiations.
  
African Union (AU) countries sent troops to Darfur in 2004 - a force which now numbers around 7000 personnel - but the mission has suffered from poor funding and has struggled to contain the violence.
  
The AU has been sponsoring inconclusive peace talks between Khartoum and Darfur rebels in Abuja, Nigeria.
  
The conflict in Darfur between rebels and militias backed by Sudanese government troops has killed some 300,000 people and displaced two million others since 2003.
  
The rebels in Darfur launched their uprising in February 2003 against what they claimed was the marginalisation of their provinces by Khartoum.