By Michelle Nichols

UNITED NATIONS (Reuters) - The U.N. Security Council demanded on Thursday that Sudan and South Sudan stop border clashes which it said threatened to return the east African neighbors to a full-scale war.

A statement from the 15-nation body also insisted that Khartoum stop air strikes and Juba withdraw troops from a vital oil field.

Fighting along the ill-defined border between the former civil-war foes has led to a standoff over Sudan's Heglig oil field after it was seized on Tuesday by troops from South Sudan, which declared independence last year.

Distrust runs deeps between the neighbors, who are at loggerheads over the position of their border, how much the landlocked south should pay to transport its oil through Sudan, and the division of national debt, amongst other issues.

"The recent violence threatens to return both countries to full-scale war and the period of tragic loss of life and suffering, destroyed infrastructure, and economic devastation, which they have worked so hard and long to overcome," a statement from the Security Council said.

"The Security Council demands a complete, immediate, and unconditional: end to all fighting; withdrawal of (South Sudan's Army) from Heglig; end to (Sudanese Armed Forces) aerial bombardments; end to repeated incidents of cross-border violence between Sudan and South Sudan; and an end to support by both sides to proxies in the other country," it said.

The Council demanded that both countries redeploy their forces 6 miles outside a north/south borderline determined in 1956 and take immediate steps to establish a safe demilitarized border zone.

It termed the situation a "serious threat to international peace and security" and warned it would take further steps as necessary, but gave no details on what those might include. Continued...