Armed men kidnapped Irish national Sharon Commins and Ugandan Hilda Kawuki from the offices of the Irish aid group GOAL in the north Darfur city of Kutum on 3 July.
Senior officials say efforts to secure their release "are ongoing".
"We will continue to be unsparing in our efforts," John O'Shea, GOAL's president, said on 24 July.
The kidnapping was the third such act directed at foreign aid workers since the ICC arrest warrant.
However, officials have said the kidnappers are bandits wanting money, and previous cases ended with the hostages being released. But it has raised concerns.
“We are worried for them – and for others in the future in Darfur,” said an aid worker. “Are they really bandits, or is this one more way to intimidate aid workers?”
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