The International Criminal Court on Tuesday gave Libya until January 23 to mull the possible handing over of ousted leader Moamer Kadhafi's son Seif al-Islam.
A three-judge bench granted a Libyan request for an extension but said that the three weeks sought by Tripoli "would cause an undue delay in the proceedings and that only a shorter extension is appropriate".
The Hague-based tribunal ordered Libyan authorities to file its observations regarding Seif al-Islam, who is wanted by the court on charges of crimes against humanity, by 1500 GMT on January 23.
ICC judges last month called on Libya's new leaders to inform them as a matter of urgency if and when they intend to hand over Seif and set a January 10 deadline for a response.
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But in a letter on Monday, Libya asked for a three-week extension.
"Due to the security situation on Libya, the Libyan authorities are not able to meet the deadline and respectfully request the chambers to grant an extension for an additional period of three weeks," it said.
The ICC issued a warrant in June for Seif on charges of crimes against humanity over the conflict in Libya, but after his capture the National Transitional Council said it wanted to try him on Libyan soil.
Seif, 39, who was arrested on November 19 -- almost a month to the day after his father was captured and killed -- is now in the custody of the military council of Zintan 180 kilometres (110 miles) southwest of Tripoli.
Human rights organisations have called on the Libyan authorities to grant him access to a lawyer, but said he appeared to be held in good conditions.