Saif al-Islam, one of Moammar Gadhafi's sons, was captured in November. He is subject to an arrest warrant issued by the ICC
The ICC said it had evidence civilians were attacked in their homes, demonstrators were fired on with live ammunition and snipers were used to kill those leaving mosques after prayers in Libya.
Libya's new government said it wanted more time to comply with the ICC regarding the arrest of Gadhafi's son because of the "security situation" in the country. The original deadline to comply was Tuesday.
"Considering that given the prevailing political and security situation in Libya, good cause is shown to necessitate the extension of the time limit to submit observations," the court said in a Tuesday judgment. Tripoli, the court said, now has until Jan. 23 to comply.
Human Rights Watch said its representatives visited Saif al-Islam at a detention center in Zintan, Libya, last month.
The rights group said he told them he was treated well by Libyan authorities and receiving food and medical care. His primary concern was the lack of access to legal counsel.
Moammar Gadhafi was captured and apparently killed by rebel forces in October. The case against him at the ICC was dropped after his death was confirmed. Former intelligence chief Abdullah al-Senoussi remains at large.