"The Army was entrusted with protecting Sudan's territory and stability and the security of its citizens in the south and north," Bashir's ruling National Congress Party said.

The southern Sudanese government warned that Khartoum's invasion of Abyei could spark another war. Officials said the southern Sudanese army has been placed on alert.

"We didn't declare war," southern army spokesman Col. Philip Aguer said. "The National Congress Party and the Sudan Armed Forces declared war on us."

In late 2010, the United Nations agreed to postpone a referendum on the future of Abyei. The remaining UN-organized referendum concerned southern Sudan, in which 95 percent voted for secession in January 2011. Secession for the south is scheduled for July 9.

Over the last two months, tensions increased steadily in Abyei. On May 19, an estimated 15 Sudanese Army soldiers were killed in an ambush in Abyei, allegedly conducted by southern units. Hours later, Bashir ordered air strikes on Abyei.

Bashir's military is said to have conducted two days of air strikes on Abyei. On May 21, the Sudanese Army, backed by main battle tanks and mortars, invaded the oil-rich region and drove out southern forces as well as most civilians. Officials said a division was deployed in Abyei.

"The event is a long-term plan done by the government of Khartoum to disrupt and carry out an invasion," Southern Sudanese Information Minister Barnaba Benjamin.

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