"We have found out that Gaddafi is now several kilometres southwards of Sirte. He is constantly moving," Anis Sharif said.
He also said Gaddafi was probably looking for a corridor to escape to Sabha, one of the few Libyan cities controlled by forces loyal to him.
"Death, suicide or a trial for Gaddafi - is a matter of time. And he's got little time left," Sharif said.
Chairman of the rebel council, Mustafa Abdel Jalil, had earlier given a one-week ultimatum to Gaddafi loyalists to leave the cities of Sirte, Sabha and Bani Walid. The ultimatum expires Sep 10.
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