U.S. Secretary of State Hillary Clinton is 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 pledging millions of dollars in new aid for educational programs, medical care for wounded fighters and archeological programs. Money will also go toward locating and destroying thousands of unaccounted shoulder-fired missiles to prevent them from entering the hands of militants.

U.S. officials say American aid to Libya since the conflict began now totals $135 million.

Clinton met with interim prime minister Mahmud Jibril and National Transitional Council chairman Mustafa Abdel Jalil during her visit. She is the most senior U.S. official to visit Tripoli 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 Bani Walid, 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 Tripoli.