"The United States urges all parties to exercise restraint," said State Department spokesperson Victoria Nuland in a statement.
The State Department was responding to reports from South Sudan that its former foe Sudan had bombed oil fields in a dispute over oil transit fees. Now independent South Sudan has to pump its oil from southern fields to a Red Sea port through northern pipelines and must pay transit fees to Sudan, Voice of America said.
The two countries separated peacefully in July after decades of civil war.
A South Sudan government spokesman said oil production was shut down Wednesday after two Sudanese jet fighters bombed oil fields in Unity state, damaging two wells and two vehicles. Production shut down in January when South Sudan accused Sudan of stealing its oil.
"These oil fields that they are targeting are about 75 kilometers (46.6 miles) from our borders with the Republic of Sudan," South Sudan spokesman Barnaba Marial Benamin told VOA. "It means they have flown into our territory about 74 kilometers, and that is violating the airspace and territorial integrity of the Republic of South Sudan."
Sudan has denied any responsibility for the bombing. South Sudan said it would bring up the issues of oil, debt relief and contested borders at the next round of African Union talks in Ethiopia next week.