Libya’s rebel movement launched mass demonstrations Friday, as it seeks to solidify its gains and pry the longtime leader’s grip on the capital. Foreign mercenaries and Libyan militiamen loyal to Gadhafi have fought hard to weaken the uprising against his rule, attacking two nearby cities Thursday in battles that killed at least 17 people. But rebels made new gains, seizing a military air base. Col. Gadhafi blamed Osama bin Laden for the upheaval.