Ban Ki-moon, the UN secretary-general, has condemned an attack on a convoy of an African Union-UN peacekeeping force in Darfur that resulted in the death of three Senegalese peacekeepers.

Ban described Sunday's incident, the second deadly attack in three days, as unacceptable and called on the Sudanese government to bring those responsible to justice.

"The Secretary-General offers his condolences to the families and friends of the fallen peacekeepers and expresses his deepest sympathies to the Government of the Republic of Senegal," the UN chief's spokesperson said in a statement.

The attack happened when a police unit escorting a water convoy from El Geneina town to the peacekeepers' regional headquarters in West Darfur was ambushed by an unidentified armed group, UNAMID, the peacekeeping mission, said in a statement.

Three peacekeepers were killed and one injured when gunmen swooped on the convoy. The attack came just two days after assailants killed a Zambian military observer in the main North Darfur city of El Fasher.

'Grave criminal act'

UNAMID did not identify the group behind the latest attack.

UNAMID Joint Special Representative Mohamed Ibn Chambas called the attack "a grave criminal act" and commended the Sudanese uniformed services for pursuing the unidentified gunmen and engaging them in a fire-fight.

He urged the Sudanese government to bring the perpetrators to justice, and thanked local authorities for pursuing the attackers and engaging them in a firefight said to have wounded people on both sides.

The Darfur war started when local groups launched an uprising in 2003 against the Arab dominated Khartoum government.

Government forces were accused of launching a brutal repression that led to war crimes and genocide charges against President Omar al-Bashir and other Sudanese officials.

The UN says at least 300,000 people have died in the conflict, a claim the Sudanese government rejects.

Hundreds of people have died in a surge of fighting during the past year that authorities and experts largely blame on rivalry between Arab tribes acting outside government control. 

UN peacekeepers have often been attacked for their vehicles and weapons.

Source: Al Jazeera and agencies