Islamic State suicide bombings kill troops in Iraq's Anbar
At least 17 Iraqi soldiers have been killed in a series of suicide attacks by Islamic State (IS) militants in Anbar province, security officials say.
The militants reportedly launched a wave of bombings outside the IS-held city of Falluja on Tuesday night.
The attacks came hours after pro-government forces began an operation to drive the jihadists out of Anbar.
On Wednesday, troops and militiamen were said to have taken up positions south of the provincial capital Ramadi.
The city was captured two weeks ago after troops withdrew despite vastly outnumbering the IS forces attacking, prompting the US defence secretary to question their "will to fight".
A source in the Iraqi army's 1st Division told the BBC that 17 of its soldiers were killed in an attack on its headquarters 5km (3 miles) east of Falluja that involved three suicide car bombs.
The source added that suicide car bombs and militants wearing explosive vests were also used to attack troops and Shia militiamen north of the town of Karma, also east of Falluja.
In both cases, the militants took advantage of a sandstorm that engulfed most of Iraq on Tuesday night to get close to their targets.
Jihadists were also besieging troops stationed at one of the locks along the canal connecting Lake Tharthar with the River Euphrates, the source said.
Meanwhile, an Iraqi army colonel told the AFP news agency that troops and fighters from the Popular Mobilisation (al-Hashd al-Shaabi), a force comprising dozens of mostly Shia militias and some Sunni volunteers, had taken up positions on the southern edge of Ramadi, outside the city's ring road.
They took control of the southern districts of Taesh and Humayra and also managed to enter the campus of the University of Anbar, the colonel said.
On Tuesday, a spokesman for the Popular Mobilisation announced that an operation to regain control of Anbar had begun and that pro-government forces would seek to encircle Ramadi before launching an assault to retake it.
The spokesman said the operation would be called "Labayk ya Hussein" ("At your service, O Hussein") - a reference to one of the most revered imams of Shia Islam.
A US defence department spokesman said the choice of name for a military campaign taking place in a predominantly Sunni Muslim province was "unhelpful".
The key to victory against IS would be a unified Iraq "that separates itself from sectarian divides, coalesces around this common threat", Col Steve Warren added.
The US has previously urged the Shia-led government not to send Shia militias to Anbar in case they drove more of Anbar's Sunnis into supporting the jihadists.
IS exploited widespread Sunni anger at the previous administration sectarian policies to seize control of Falluja and parts of Ramadi in January 2014.