An indiscriminate attack on civilians in Benghazi would constitute "war crimes", the prosecutor of the International Criminal Court warned the Libyan government today.

"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, his sons and key aides for crimes against humanity arising from the bloody crackdown on Libya's popular revolt.

The UN Security Council late yesterday 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.

Libyan leader Muammar Gaddafi warned in a television address that his troops would launch an assault on Benghazi on Thursday night and show "no mercy".

But Moreno-Ocampo said a government ultimatum to Benghazi citizens to leave the areas to be attacked 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," he said.

"If this happens, I will present a case against them. There will be no impunity."

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.