Juba seized the oil hub on April 10, claiming that Khartoum was using Heglig as a base to attack the South's oil-producing Unity State. Although South Sudan disputes it, Heglig is internationally regarded as part of Sudan.
The South's occupation met widespread criticism, including from UN chief
the ephemeral Ban Ki-moon... of whom it can be said to his credit that he is not Kofi Annan...
, who called it illegal.
South Sudan's President Salva Kiir on Friday announced his forces would carry out "an orderly withdrawal" from the area. On Sunday, a Sudan People's Liberation Army (SPLA) front man said all southern troops had left.
The SPLA "completed its withdrawal from Heglig yesterday" front man Philip Aguer told AFP.
But, he charged, as the withdrawal was ongoing, Khartoum's air force "continued bombing on the night of the (Friday April) 20th and in the morning of the 21st".
The two sides have offered contradictory explanations for recent developments in Heglig.
On Friday, Sudan said its soldiers had "liberated" the oil field by force, despite, despite Kiir's earlier announcement of a withdrawal.
The South Sudanese UN Ambassador Agnes Oswaha has said Juba decided to withdraw "because it does not wish to see a return to war."