(CNN) -- A U.N. Security Council delegation arrived in Khartoum, Sudan, on Saturday to discuss with government officials the ongoing peace process in the country following a referendum in January that split the north from the south.
The visit comes two days after an attack on northern Sudanese armed forces and members of the U.N. peacekeeping mission in the disputed region of Abyei, according to state-run media.
South Sudan in January voted to split from the north, and is expected to officially become an independent nation in July.
However, the fate of the oil-rich Abyei region remains a flash point.
"Forces of the Sudan People's Liberation Army (SPLA) ambushed and attacked United Nations' forces and our forces in the Joint Integrated Units using heavy weaponry, causing great losses," read a statement issued Friday by the Sudan Armed Forces.
The attack took place in the town of Dokura, 10 kilometers (6 miles) north of Abyei, as Joint Integrated Units of the Sudan Armed Forces were redeploying to a new post as part of a previous agreement.
At least 22 people were killed, according to Sudanese army sources.
SPLA denied responsibility for the attack.
The United Nations Mission in Sudan (UNMIS) issued a statement condemning the attack.
"This act constitutes a serious breach of previous agreements made between the two parties. It is also a criminal act against the U.N.," the statement said. "UNMIS calls on all parties to investigate the incident and take appropriate action against the perpetrators of this deliberate attack."
U.S. State Department spokesman Mark Toner also expressed concern.
"Political leaders on both sides must take responsibility now to ensure that this situation does not escalate into a wider crisis," he told reporters at a press conference on Friday.
On Saturday, UNMIS issued another statement, saying it is "deeply concerned by the heightened violence and the loss of life" in the region, "resulting from the fighting of the SPLA against militia groups."
"Of regular concern are reports that civilians are being targeted, including by use of heavy caliber weapons and land mines," the statement said. "Such actions constitute serious violations of basic human rights and international law."
The U.N. said this month that violence in the Abyei region will jeopardize relations between the north and South Sudan governments as the two sides gear up for a permanent separation July 9.
Journalist Ismail Kushkush contributed to this report.