BAGHDAD, May 21 (Reuters) - Islamic State militants overran Iraqi government defenses east of the city of Ramadi on Thursday, police and pro-government tribal fighters said.
The defensive line was breached at Husaiba, about 10 km (six miles) from the city, on Thursday afternoon after IS fighters intensified mortar and rocket fire.
"The situation is very critical now after Daesh (IS) fighters managed to overrun our defensive line in Husaiba," Police major Khalid al-Fahdawi said.
"We have retreated to the eastern part of the area and we're waiting for more reinforcements and air force strikes to stop the Daesh advance."
Ramadi fell to the insurgents on Sunday in the most significant setback for Iraqi security forces in nearly a year.
The IS advance has exposed the shortcomings of Iraq's army and the limitations of U.S. air strikes.
Islamic State is seeking to consolidate its gains in the vast desert province of Anbar, of which Ramadi is capital, where only pockets of territory remain under government control.
Government forces backed by Shi'ite militias have meanwhile been building up at a base near Ramadi in preparation for a counterattack to retake the city.
Sunni Islamic State forces there have taken over tanks and artillery and large amounts of ammunition abandoned by fleeing Iraqi forces.