The Press Secretary of the White House released a statement on Sudan on May 21, 2011. The statement said, "The United States condemns the offensive operations being undertaken by the Sudanese Armed Forces (SAF) in and around Abyei town and today's Presidential decree dissolving the Abyei Administration. While the United States deplored the May 19 attack by Southern forces on a United Nations convoy that was transporting a SAF company lawfully operating as part of the Joint Integrated Units in Abyei, this response is disproportionate and irresponsible. The actions being taken by the Government of Sudan are blatant violations of the Comprehensive Peace Agreement and threaten to undermine the mutual commitment of the CPA parties to avoid a return to war.
"The United States calls on the SAF to immediately cease all offensive operations in Abyei and withdraw its forces from Abyei. Failure to do so could set back the process of normalizing relations between Sudan and the United States and inhibit the international community's ability to move forward on issues critical to Sudan's future. Both sides must follow through with implementing the Kadugli Agreements of January 13 and 17, including the withdrawal of all unauthorized forces in Abyei. The United States calls on President Bashir and First Vice President Kiir to meet immediately and agree on a way forward that restores calm, upholds the CPA, and recommits both sides to a negotiated political settlement on the future status of the Abyei Area."
You can also read the statement here.