CAIRO — Libyan protesters seeking to oust longtime leader Muammar Gaddafi defied a crackdown and took to the streets in five cities Thursday on what activists have dubbed a "day of rage," amid reports at least 20 demonstrators have been killed in clashes with pro-government groups.New York-based Human Rights Watch said Libyan internal security forces also have arrested at least 14 people. Hundreds of pro-government demonstrators also rallied in the capital, Tripoli, blocking traffic in some areas, witnesses said.An opposition website and an anti-Gaddafi activist said unrest broke out during marches in four Libyan cities — Beyida, Benghazi, Zentan, Rijban and Darnah. Organizers were using social networking sites like Facebook and Twitter to call for nationwide demonstrations."Today the Libyans broke the barrier or fear, it is a new dawn," said Faiz Jibril, an opposition leader in exile.