The United Nations mission in Sudan said it had received reports of a rebel attack, and there were reportedly casualties on both sides.
"The armed forces have countered a treacherous attack led by forces belonging to the Justice and Equality Movement (JEM) and the Beja Congress, backed by foreign parties, against the outpost of Dolibo-Yei of the Toker military garrison at 1300 on Sunday," a military statement said.
The JEM is one of the Darfur rebel groups currently conducting peace talks with the Khartoum government through African Union mediation in the Nigerian capital of Abuja.
Its spokesmen could not be reached for comment.
The Beja Congress is a rebel group from the Beja tribe in eastern Sudan. Beja members have recently staged anti-government demonstrations in the Port Sudan area.
The Toker garrison lies south of Port Sudan, the main city on Sudan's Red Sea coast.
In its Sudan situation report on Monday, the UN mission said reports on Sunday indicated that "Beja Congress attacked an army post in Delabiyay. The army managed to repel the attack".
The UN said nothing about any involvement by the JEM. It said UN-rented trucks carrying food had been in the area at the time of the attack, but they emerged unscathed.
The Sudanese military statement did not name the "foreign parties" whom it claimed to be backing the rebels, but Sudan has recently accused its southeastern neighbour, Eritrea, of supporting the rebel forces.
The government refused to allow Eritrea to be part of the mediating team at the Abuja peace talks.
The statement said the armed forces were able to "completely control" the attack and were now pursuing the rebels.
It added that government forces suffered no casualties and gave no figure for rebel casualties.