The protesters reportedly took over al-Jawf, which borders Saudi Arabia in the northeast on Monday. Three soldiers were killed during clashes in the city.
Protesters also took control of Marib, east of the capital, Sana’a, where several oil and gas fields run by international companies are located.
Earlier reports said Marib Governor Ahmed Naji al-Zaidi was attacked and wounded during an anti-government protest outside the local government headquarters. He is currently receiving treatment in Sana’a.
Meanwhile, one of Yemen’s largest tribal federations, Baqil, joined the protesters in the capital’s Change Square.
Two high-ranking officers have also joined the protesters.
This comes as Yemeni police have intensified the crackdown on demonstrators. Security forces have surrounded a protest camp in Sana’a.
At least 40 people were injured in the capital after police opened fire on protesters on Monday.
One-hundred others were also wounded on Sunday after police on rooftops fired live rounds and teargas on people, camping near Sana’a University.
Heavily armed troops have also been deployed in the southern city of Aden.
Protesters are calling for President Ali Abdullah Saleh to step down after 32 years in power.