Washington, Apr 5 (IANS): The US has called on Sudan and South Sudan to show restraint following reports that South Sudan shot down a Sudanese fighter jet.

"We're calling on restraint on the part of all sides. And we're very concerned about the ongoing hostilities on the border areas between South Sudan and Sudan," Xinhua quoted State Department spokesman Mark Toner as saying.

"We call upon the parties to cease fighting and ensure the safety and security of civilians, first and foremost, and then negotiate a solution to grievances under the auspices of the African Union," he said.

Sudanese army denied as baseless reports that its military plane was shot down by South Sudan army in Unity State of South Sudan, the official SUNA news agency reported.

Sudanese military spokesman Al-Sawarmy Khalid Saad said the army does not use such planes.

Earlier, South Sudan military spokesman Philip Aguer said the country's forces have shot down a Sudanese MiG-29 military plane Wednesday afternoon, which, together with another plane, was flying over its oil fields.

According to Xinhua, the incident, if turns out to be true, would signal a further escalation of tensions after military clashes erupted last week at the border area of Higlieg.

The grievances have largely resulted from a number of unresolved issues, including the demarcation of border and the division of oil revenue, since South Sudan was declared independent in July last year.