The majority of the voters who took part in a January referendum backed a measure that gives South Sudan the right to become an independent state. The referendum was part of a comprehensive peace deal reached with Washington's help in 2005, though border issues threaten to unravel the peace initiative.
Both Sudanese governments during bilateral talks in Addis Ababa agreed Ethiopian forces would deploy to the Abyei region in exchange for withdrawal from rival Sudanese military factions.
The U.N. Security Council in Resolution 1990 sanctioned the measure that calls for the deployment of up to 4,200 Ethiopian peacekeepers.
Conflict in Abyei, however, has spilled over to South Kordofan state, situated along the border between the northern and southern regions of Sudan. The U.S. State Department said while the Ethiopian force was welcomed, more was needed to secure the peace.
"We urge the parties to reach an immediate cease-fire and to provide aid workers with the unfettered access required to deliver humanitarian assistance to innocent civilians affected by the conflict," a statement read.
South Sudan becomes Africa's newest independent state July 9.