If a country is not a member of the International Criminal Court (such as Libya and Sri Lanka), its citizens can be prosecuted by the ICC for crimes against humanity, war crimes, or genocide only if the UN Security Council refers it.
The below are extracts from UNSC resolution 1970 (2011) related to the referring of Libya to the ICC:
“The Security Council,
“Recalling article 16 of the Rome Statute under which no investigation or prosecution may be commenced or proceeded with by the International Criminal Court for a period of 12 months after a Security Council request to that effect,
“4. Decides to refer the situation in [Libya] since 15 February 2011 to the Prosecutor of the International Criminal Court;
“5. Decides that the Libyan authorities shall cooperate fully with and provide any necessary assistance to the Court and the Prosecutor pursuant to this resolution and, while recognizing that States not party to the Rome Statute have no obligation under the Statute, urges all States and concerned regional and other international organizations to cooperate fully with the Court and the Prosecutor;
“6. Decides that nationals, current or former officials or personnel from a State outside the [Libya] which is not a party to the Rome Statute of the International Criminal Court shall be subject to the exclusive jurisdiction of that State for all alleged acts or omissions arising out of or related to operations in [Libya]established or authorized by the Council, unless such exclusive jurisdiction has been expressly waived by the State;
“7. Invites the Prosecutor to address the Security Council within two months of the adoption of this resolution and every six months thereafter on actions taken pursuant to this resolution;
“8. Recognizes that none of the expenses incurred in connection with the referral, including expenses related to investigations or prosecutions in connection with that referral, shall be borne by the United Nations and that such costs shall be borne by the parties to the Rome Statute and those States that wish to contribute voluntarily;
The resolution won a rare unanimous endorsement on Saturday from the UNSC's 15 members, including India, China and Russia.
See also, comments by UN Secretary-General Ban Ki-Moon and the representatives of these and other countries presently on the Council here (at the bottom).