Summary:
Two people have been killed and nine others injured in clashes in northern Yemen, witnesses say.

Full article:
Harf Sofyan, Yemen (CNN) -- Security forces opened fire on anti-government protesters in northern Yemen on Friday morning, killing two people and injuring nine others, witnesses said. The forces fired into the protesters in Harf Sufyan city to try and disperse them, witnesses said. Three army planes flying over the crowd also attacked the protesters, witnesses said. The vast majority of the protesters were Houthi rebels, according to Mohammed Abdulsalam, a spokesman for the group . Since 2004, the Houthis have waged a separatist  revolt over who which religious sect will control the area. The Houthis are Shiite Muslims and followers of slain Shiite cleric Hussein al-Houthi. The majority of Yemenis are Sunnis. Elsewhere in Yemen on Friday,  thousands of anti-government demonstrators in Sana'a called for President Ali Abdullah Saleh  to step down as they continued to hold a sit-in demonstration outside Sanaa University. The crowd included students, women, tribesmen and members of the opposition In Aden Province. Thousands also continued to demonstrate against Saleh's regime in the provinces of Taiz, Mareb and Jawf. Hakim Almasmari contributed to this report.