Unidentified gunmen shot and wounded four Zambian peacekeepers belonging to the UN Mission in Sudan (UNMIS), who were on patrol in Sudan's Abyei area, UNMIS said in a statement on Wednesday.

The shooting took place on Tuesday afternoon in Goli, some 25 km north of Abyei town, the statement said, adding the four peacekeepers, one of whom in serious condition, have been taken to Abyei town for treatment.

"UNMIS strongly condemns this unprovoked attack and has commenced an investigation into the incident," the statement said.

The attack came after an agreement reached between north and south Sudan governments to withdraw all their forces unauthorized to be deployed at the disputed Abyei area and to implement a security agreement inked earlier under the support of the African Union.

Sudan's north and south are yet to solve the conflict over oil-rich Abyei where tension increased after a referendum in January 2011, resulting in the separation of south Sudan.

The south Sudan government earlier said it intended to include the Abyei area in the proposed constitution of south Sudan, which pushed Sudanese President Omar al-Bashir to threaten not to recognize a south Sudan state if Abyei is included in the constitution.

South Sudan is expected to officially be declared independent on July 9, but many thorny issues, including Abyei, are still outstanding between north and south Sudan, which prompts concerns over possibility of future armed clashes between the two sides.