The Iraq government has lost control of the strategic city of Fallujah, west of Baghdad, say officials and witnesses.
Al-Qaeda-linked militants now control the south of the city, a security source told the BBC. An Iraqi reporter there says tribesmen allied with al-Qaeda hold the rest of Fallujah.
Fighting there erupted after troops broke up a protest camp by Sunni Arabs in the city of Ramadi on Monday.
They have been accusing the Shia-led government of marginalising the Sunnis.