Misurata's phones, electricity and water were cut off as government forces shelled the city with artillery and massed tanks for a ground assault, The New York Times reported, citing residents.
The situation in Ajdabiya was murky. Rebels denied Gadhafi's forces have taken the city, and the Times reported claims that rebels recaptured part of it Tuesday night.
Meanwhile, the BBC reported government soldiers have begun their initial ground assault on Benghazi, the opposition's headquarters.
French Foreign Minister Alain Juppe wrote on his blog Wednesday that several unnamed Arab nations had offered to intervene in support of the rebels. France and Britain have called for airstrikes on Gadhafi's forces, but other European nations oppose them.
The U.N. Security Council is considering a no-fly zone over Libyan airspace in response to the rebels' pleas. Britain, France and Lebanon have drafted such a resolution, but the United States, Russia, China and Germany are wary.
A senior U.S. official told the Times there is increasing consensus in the White House that it is too late to set up a no-fly zone, and other options to help the rebels are being considered.
The Arab League also supports a no-fly zone, but Group of Eight ministers Tuesday failed to endorse the idea.
Jalal al-Gallal of the National Libyan Transitional Council in Benghazi told the BBC a "massacre" would result if the international community does not intervene to stop Gadhafi.
"He will kill civilians. He will kill dreams. He will destroy us," he said.
In a televised speech, Gadhafi challenged the United States, Britain and France to "give their people freedom like I did to the Libyan people."
The speech was projected upside down onto a screen in the main square of Benghazi, where people threw shoes as an expression of contempt for Gadhafi, the BBC said.
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