U.S. Secretary of State Hillary Clinton has arrived in Libya for a previously unannounced visit with the country's new rulers, while Libyan provisional government fighters launch an assault on one of the last remaining strongholds of former leader Moammar Gadhafi.

Clinton arrived Tuesday in the capital of Tripoli, where she is expected to pledge millions of dollars in new aid for educational programs, medical care for wounded fighters, weaponry assistance and archeological programs.

Clinton is expected to meet with Transitional National Council chairman Mustafa Abdel Jalil and interim prime minister Mahmud Jibril during her visit. It is the highest level visit by an American official since the uprising against Mr. Gadhafi began in February.

Meanwhile, hundreds of Libyan government fighters on Tuesday carried out an attack on the coastal city of Sirte, a day after saying they captured the only other remaining Gadhafi loyalist stronghold.

Pro-Gadhafi fighters have been hemmed into a small area of Sirte, where National Transitional Council forces have tried for weeks to gain control. NTC officials have said capturing Mr. Gadhafi's hometown would allow them to declare their country liberated.

On Monday, NTC officials said the desert town of Bani Walid was completely free of pro-Gadhafi fighters. Provisional government forces had launched a new assault Sunday on the town, about 170 kilometers southeast of the capital, Tripoli.