Unidentified gunmen have launched two attacks on peacekeepers in Sudan's troubled Darfur region, losing four of their own men in one of them, the UN-African Union mission said on Friday.
The UN-AU mission in Darfur deployed to the region in 2007, four years after ethnic insurgents mounted a campaign against the Arab-dominated government of Omar al-Bashir, complaining of their marginalisation.
Around 40 horsemen and camel-mounted gunmen attacked "Nigerian troops protecting a water point" in Kass, 85 kilometres (53 miles) from South Darfur state capital Nyala, on Thursday evening.
The peacekeepers returned fire, killing four attackers and wounding one, whom they handed over to Sudanese police, UNAMID said.
Two peacekeepers were also wounded, it said.
On Friday morning, unidentified gunmen attacked a UNAMID patrol travelling from Nyala to Kass and "four peacekeepers were injured during the exchange of fire", the mission said.
UNAMID acting head Abiodun Bashua called on Khartoum to investigate the attacks.
"The continuing climate of impunity and failure to prosecute those who attack peacekeepers and humanitarian workers have to end," Bashua said in a statement.
However, last year Khartoum told UNAMID to prepare to leave after the mission's attempts to investigate the reported rape of 200 women and girls in a North Darfur village sparked government anger.
Talks between the UN, AU and government on an exit strategy for the mission are due to resume in the second week of May.
Gunmen sporadically attack UNAMID patrols in Darfur. Three Ethiopian peacekeepers were killed last October as they guarded a well in North Darfur.
Since the conflict in the western region erupted in 2003, 300,000 people have been killed and nearly 2.5 million more forced to flee their homes, the UN says, although the government puts the death toll at 10,000.
The International Criminal Court indicted Bashir for alleged war crimes and crimes against humanity in 2009 and for genocide in 2010.