Any indiscriminate attack on civilians in Benghazi could result in a war crimes prosecution, the prosecutor of the International Criminal Court warned the Libyan government on Friday.
"Any indiscriminate attack against civilians would constitute war crimes," prosecutor Luis Moreno-Ocampo told journalists in The Hague.
"The commanders will be responsible. As the prosecutor of the ICC, I will request an arrest warrant against them."
On March 3 Moreno-Ocampo announced a probe into Gaddafi, three of his sons and key aides for crimes against humanity arising from the bloody crackdown on Libya's popular revolt.
The probe could be expanded to include war crimes, the prosecutor said that on Friday, adding that a government ultimatum to Benghazi citizens to leave areas targeted for attack would make no difference to his analysis.
"I like to be clear: the issuance of such a warning does not provide an excuse to attack civilians," Moreno-Ocampo said.
"If this happens, I will present a case against them. There will be no impunity."
Under international law, war crimes, unlike crimes against humanity, can only be committed within the context of an armed conflict.
"The government can control rebellion but cannot attack civilians, that is in the law," said Moreno-Ocampo.
Late on Thursday the United Nations Security Council (UNSC) passed a resolution approving "all necessary measures" to impose a no-fly zone in Libya, protect civilian areas and pressure Gaddafi into accepting a ceasefire.
Gaddafi had warned in a television address that his troops would launch an assault on Benghazi and show "no mercy".
Libya shut its air space on Friday as Britain and France were expected to scramble fighter jets against Gaddafi's forces.
The prosecutor's ongoing probe of crimes against humanity follows a referral by the UNSC which said "the widespread and systematic attacks currently taking place against the civilian population may amount to crimes against humanity".
The probe of Gaddafi's "inner circle" include the regime's spokesman, the commander of the 32nd Brigade and the national security advisor, according to a prosecution document.
Moreno-Ocampo has "put on notice" a group of key Gaddafi aides, who may make themselves liable to prosecution for "not preventing, stopping or punishing these crimes".
They included the foreign minister, the head of the regime's security and military intelligence, the head of the veteran Libyan leader's personal security, and the head of the Libyan External Security Organisation.
The ICC, based in The Hague, is the world's only independent, permanent tribunal with the jurisdiction to try genocide, crimes against humanity and war crimes.