South Sudan's army says Sudan has launched attacks along the two countries' border.
SPLA commander General James Gatluak says the Sudan Armed Forces, using artillery and helicopter gunships, attacked troops Sunday in Panakuach, Unity state, injuring four people.
He says South Sudan is willing to return to negotiations, but will be in a position to defend itself if necessary.
A Sudanese army spokesman denied the bombings in comments reported by the French news agency.
On Sunday, Sudan declared a state of emergency along the border with South Sudan.
Sudan's official news agency SUNA reports the decree gives Khartoum broader powers to arrest and try suspects in the volatile region. It allows President Omar al-Bashir and "anyone with his mandate" to set up "special courts" to handle criminal and terror cases.
The measure also suspends the constitution in border areas and imposes a trade embargo against the south.
Sudan and South Sudan have lingering disputes over oil revenue and borders stemming from the south's independence last year.
The international community has called on both sides to end hostilities and resume dialogue. African Union-hosted talks to resolve the disputes have yielded little progress.