Newly-independent South Sudan has accused the north of invading its territory and occupying a town near the border.

The South Sudan government said in a statement released Wednesday that the Sudan Armed Forces attacked the town of Jaw with mechanized infantry on December 3rd and occupied it.

South Sudan said the attack led to heavy casualties and displaced a large number of civilians from the town, located in Unity state.

A team from the United Nations Mission in South Sudan visited the area Tuesday, confirming that at least 37 people were killed and 22 others wounded. Four were critically injured and taken to the country's capital, Juba, for medical treatment. The U.N. mission said it could not confirm who was responsible for the attack.

The Sudan Tribune newspaper first reported the incursion Sunday and linked it to Sudan's efforts to defeat rebels in the border states of Southern Kordofan and Blue Nile. The Sudanese government has claimed a series of victories over the rebels.

Tension between Sudan and South Sudan has run high since the south declared independence in July, after more than two decades of war.

The countries accuse each other of supporting rebels in each other's territory. Sudan seized South Sudanese oil exports last week amid a dispute over transit fees.

South Sudan said Wednesday that the north has bombed and crossed over into its territory multiple times in the past month.