Ramadi, Iraq (BBN)-Islamic State militants have seized the main government building in Ramadi, the capital of Iraq's largest province.
As many as six suicide car bombs and mortars were used in the assault on the compound that houses the main police HQ and governor's office, reports BBC.
At least 50 police officers are reported to have been taken prisoner at the site.
IS and Iraqi troops have been battling for months to take control of the strategically important Anbar province.
This latest attack comes a day after Islamic State put out an audio message it claimed was from its leader, Abu Bakr al-Baghdadi, who Iraq had said was seriously wounded in a coalition air strike in March.
The White House said on Friday US Vice-President Joe Biden had spoken to Iraq's PM Haidar al-Abadi and pledged to deliver heavy weaponry, including shoulder-held rockets and additional ammunition, as well as supplies to the Iraqi forces.
EXECUTION FEARS
IS militants launched their raid on Ramadi overnight, driving suicide car bombs into the compound housing a number of government buildings.
At least 10 police officers were killed and dozens of others wounded in the attack, officials said.
Fighting continued into Friday and by 14:00 (11:00 GMT) the black flag of IS was seen flying over the complex.
IS "now occupies the government centre in Ramadi and has also raised its flag over the police HQ for Anbar", a police major told the AFP news agency.
The militant group itself issued a statement confirming it had taken control of the complex and said it had killed an unspecified number of pro-government fighters.
Fifty police officers are known to have been taken prisoner in the assault, but reports that they have been summarily executed are unconfirmed.
Fighting is reported to be continuing in other parts of the city.
This latest assault is a blow for the Iraqi government which has been trying for more than a year to prevent Anbar and its key towns and cities from falling into the hands of IS.
The heavily-Sunni province of Anbar covers a vast stretch of the country west from the capital Baghdad to the Syrian border, and contains key highways that link Iraq to both Syria and Jordan.
Iraq's prime minister pledged in April that his forces would "liberate" Anbar from IS after the success of re-taking Tikrit.
However, by Friday, the militant group had asserted its control over large areas of Ramadi and half of Anbar province, our correspondent reports.
Meanwhile, in Syria, Islamic State militants are said to be getting close to the famous ancient ruins of Palmyra.
Syrian government forces and warplanes are trying to halt the advance of IS fighters towards the World Heritage Site.
Cultural officials fear that if IS makes it to Palmyra, they will destroy the historic ruins like they have at several other ancient sites in Iraq.
TROUBLED HISTORY OF ANBAR PROVINCE
Iraq's largest province and its only Sunni-dominated one was occupied by US forces in 2003
Hostile to the US, fighting quickly broke out between US troops and the region's Sunni insurgents
The worst battle came in 2004 when thousands died as US troops and coalition forces struggled to take the town of Falluja
Fighting continued in 2005 and 2006 during which time al-Qaeda in Iraq (AQI) rose to prominence
The US declared victory in 2007 but AQI remained, resuming attacks in 2011 when US troops withdrew
AQI, which appears to have now become the Islamic State, and other Sunni insurgents currently control much of the province