(CNN) -- Four U.N.-African Union peacekeepers are missing in the war-torn western Sudanese region of Darfur, the peacekeeping force said Monday.
The peacekeepers were last seen Sunday evening when they left Nyala, the capital of South Darfur state. They were headed to their private quarters about 4.3 miles (7 kilometers) away, said UNAMID -- a United Nations and African Union force designated to keep peace in the region.
"There have been no sightings of our staff and we are deeply concerned for their well-being," said Ibrahim Gambari, head of UNAMID.
The mission said it was working with the Sudanese government and local authorities to try to find the staffers.
Darfur has been beset by conflict since 2003. The joint mission began operations in December 2007 and has been the target of several deadly attacks since then.
The force is expected to remain in Darfur until July.
The peacekeepers disappeared the same day that millions of Sudanese headed to the polls for the country's first presidential and parliamentary elections in 24 years.
Last week, the European Union announced it was withdrawing its observers from Darfur because of security concerns, and there have been tensions between government and opposition activists during the election campaign, UNAMID said.
The violence in Darfur erupted in 2003 after rebels began an uprising against the Sudanese government.
To counter the rebels, Arab militias with ties to the Sudanese government went from village to village in Darfur, killing, torturing and raping residents there, according to the United Nations, Western governments and human rights organizations. The militias targeted civilian members of tribes from which the rebels drew strength.
The United Nations estimates that 300,000 people have been killed in the conflict in Darfur, and 2.5 million have been forced to flee their homes. Sudan denies the death toll is that high.
The International Criminal Court has issued an arrest warrant for Sudanese President Omar Hassan al-Bashir, accusing him of war crimes and crimes against humanity -- charges he denies.
He is running for the presidency in the current elections.