Witnesses and a South Sudanese official say Sudanese warplanes have carried out airstrikes on a border area of neighboring South Sudan, killing at least one person.

The deputy head of South Sudan's military intelligence called the bombings Monday near Bentiu a “serious escalation” and a “clear provocation.”

Reporters who witnessed airstrikes said the attack killed a young boy at a market.

The bombings come a day after South Sudanese troops completed their withdrawal from the flashpoint town of Heglig, a contested oil-producing area where they seized oil fields on April 10.

The international community has pressed both countries to halt cross-border attacks and restart dialogue.

The two sides have given conflicting reports of casualties during the battle for Heglig, with Sudan saying 400 South Sudanese troops were killed and South Sudan saying the number is a fraction of what Sudan claims.

The north and south signed a peace deal in 2005, ending a 21-year civil war that killed more than two million people. The deal included an independence referendum for the south, which split from the north last July.

The two countries have been unable to resolve disputes over borders, oil and citizenship.