South Sudanese forces will not leave an oilfield vital to the northern economy until the threat of cross-border attacks by Khartoum is removed, the south's information minister said on Thursday.

Sudan said on Wednesday it would mobilise its army against South Sudan and halted talks with the southern government over oil payments and other disputed issues after the South occupied the border region oilfield. The south said it did so to put an end to attacks from the north.

"There must be a mechanism so they don't launch another attack," South Sudan's Information Minister Barnaba Marial Benjamin cited President Salva Kiir as saying.

He said Sudan's air force had dropped six bombs on Unity State on the southern side of the ill-defined border on Thursday, killing one soldier.