Sudanese warplanes dropped several bombs wounding four soldiers in a contested area claimed by South Sudan, breaking a fresh non-aggression pact between the two sides, Juba's army spokesman said Tuesday.

"Sudanese Armed Forces airplanes bombed the Jau area in Unity state on Sunday, wounding four of our soldiers," South Sudanese army spokesman Philip Aguer told AFP.

South Sudan -- which declared independence from former civil war enemies in north Sudan in July -- has accused Khartoum of carrying out several bombing raids in frontier regions of its territory, claims denied by the northern army.

The bombings took place in oil-rich areas along the disputed border with the rump state of Sudan, which both sides claim as theirs. The Jau area has seen several bombings in recent months as well as fighting between the two sides.

"There were several bombs launched from Antonov aircraft," Aguer said.

The region borders Sudan's Southern Kordofan state where rebels -- once part of the ex-guerrilla turned official South Sudanese army -- are battling the Khartoum government forces.

Sudan and South Sudan signed a non-aggression pact late Friday over the disputed border in the Ethiopian capital Addis Ababa, a move praised by UN Secretary General Ban Ki-moon.

However, Aguer said the latest bombings showed the deal had not been taken seriously by Khartoum.

"Nothing has changed, it is business as usual for them," Aguer said.

Gideon Gatpan, minister of information for Unity state, confirmed there had been "several bombings" on Sunday in the Jau area.

According to the pact, the two sides agreed to "respect each other's sovereignty and territorial integrity" and to "refrain from launching any attack, including bombardment."

Border tensions have mounted since South Sudan split from Sudan in July, becoming the world's newest nation.

South Sudan took three quarters of Sudan's oil when it gained independence, but all pipeline and export facilities are controlled by the north.

Last month, the South halted oil production -- accounting for 98 percent of government revenue -- after Juba accused Khartoum of stealing $815 million worth of crude oil.

The latest round of talks between Khartoum and Juba continue in Addis Ababa to resolve the furious oil crisis.

The UN chief last week warned that tensions between the two nations could escalate if outstanding issues are not resolved.

However, the South has demanded that a deal includes settlement on the undemarcated border, parts of which cut through oil fields, as well on Abyei, a Lebanon-sized region claimed by both sides but occupied by northern troops.

At least 105,000 Sudanese refugees have fled into South Sudan since fighting erupted in the states of Southern Kordofan and Blue Nile last year, after Khartoum moved to assert its authority in the wake of southern secession.

The refugees are adding to the woes of the grossly impoverished South, which is reeling from internal crises including a wave of bloody ethnic violence, rebel attacks and severe food shortages.

In addition, Juba is struggling to support over 364,000 people who have returned to their homeland since October 2010 from the north, where they fled during the war.

An estimated 700,000 ethnic southerners remain in north Sudan, where aid officials are increasingly concerned for their future, with an April 8 deadline approaching for them to either register or leave Sudan.