By Babak Dehghanpisheh and Michael Georgy
KIRKUK, Iraq (Reuters) - At least 100 fighters sneaked into Kirkuk in the early hours of Friday with machine guns, rocket propelled grenades, suicide vests and a message: "Islamic State has taken over."
The message blared out from several mosque loudspeakers while the militants went on a rampage.
By the time they had blasted their way across the city in a brazen and complex attack, 99 civilians and members of the security forces were dead and 63 of their own were in the morgue, according to Iraqi security officials.
The scale of the operation - the largest of several by Islamic State to divert an advance on their stronghold in Mosul - shows how tough the battle for Mosul may become and points to a continued ability of the militant group to undermine security across the country even if its northern bastion falls.
Accounts gathered by Reuters from residents, police, security and intelligence officials suggest it was carried out by forces that were highly trained, well-prepared and - alarmingly for the government - supported from inside Kirkuk.
"What was surprising is it was done so easily," said Ranj Talabani, a senior Kurdish intelligence official.
Like the Islamic State attacks on Paris last year, the operation appeared aimed at spreading chaos and fear rather than seizing territory. Although the heaviest fighting was over by Friday night, clashes continued for two days and officials are still searching for Islamic State units in the city.
The blackened and bullet-ridden facade of two hotels near Kirkuk's governorate building, one of the targets of the attack, are a clear sign of its ferocity. The smell of smoke and cordite still linger.
Kirkuk, 100 km (60 miles) southeast of Mosul, is close to oilfields which hold much of Iraq's vast crude reserves. It also lies near northern Iraq's semi-autonomous Kurdish region, and has been controlled by Kurdish forces since the Iraqi army retreated from advancing Islamic State forces in 2014.
The attack took place four days after the launch of an offensive against Islamic State in Mosul by Kurdish peshmerga, Iraqi soldiers and a U.S.-led international coalition.
The fighters appeared well-trained for urban combat, a sign that the battle for Mosul, Iraq’s second largest city, could be drawn-out and bloody, according to Iraqi security officials.
"These were the most professional fighters that I have seen since 2003," said Halo Najat Hamza, director of the Asayesh, a Kurdish security and intelligence force, in Kirkuk.
On Sunday afternoon, two and a half days after the attack began, two snipers detonated their suicide vests during a heavy exchange of fire with security forces at an elementary school. But no local official was prepared to say the attack was completely over.
"We are still hunting them," said one Kirkuk official who asked not to be identified for security reasons.
The operation was not improvised: a video found on a Samsung Galaxy phone on the body of a fighter shows footage of targets around the city filmed before the attack.
"It involved a lot of preparation," said Iraq's former finance and foreign minister Hoshiyar Zebari, a Kurd.
The operation began at approximately 3 a.m. on Friday morning, when fighters arrived in pickup trucks and were dropped off on the southern perimeter of the city.
The group broke up into 20 teams of five and fanned out across the city on foot. Several teams worked together to attack the first two targets: a base for the Asayesh and a police station in southern Kirkuk.
A ferocious gunbattle broke out at both locations. "They looked wild," said Hamza.
He described the fighters as having long beards, long hair and "Afghan robes", although Iraqi security officials say they did not find any documents on dead fighters to suggest they were foreign combatants, and local people who encountered the fighters said they spoke a local Iraqi Arabic dialect.
At around 4 a.m. two teams of snipers reached the center of the city and broke up, one group headed to the rooftop of the Senobar hotel and the other headed to the Dar al Salam hotel across the street. Both hotels were closed for repairs.
Their target was a few hundred meters away across a roundabout: the Kirkuk governorate building.
At approximately the same time, fighters shot their way through door locks and took over two houses in an adjacent neighborhood, demanding residents give them shelter and asking for keys to their cars.
Video footage from one of the houses shows fighters in south Asian-style shalwar kameez clothing, toting machine guns, an RPG and several reserve clips of ammunition.
One fighter is seen running to the head of the street next to the Senobar hotel and shooting off an RPG at the governorate building which explodes in a ball of fire and sparks.
A few blocks away at the Kirkuk general hospital, Samim Hamza, a policeman, heard the explosions and machinegun fire. "It was obvious this wasn’t an ordinary attack," said Samim, who lost five police colleagues in the attack.
At the time the clashes were spreading out across Kirkuk, four Islamic State militants wearing suicide vests also attacked a power station in the town of Dibis, 30 km away. At least 11 people were killed, among them three Iranian engineers who had been working at the plant.
Back in Kirkuk, sleeper cells in the city helped the fighters, according to Iraqi security officials and a U.S. military official. Residents report seeing cars driving up near the Senobar hotel during the clashes and dropping off ammunition for the fighters.
By daybreak, gunfire and explosions reverberated across the city, as the jihadists fought street battles with security forces and snipers picked off targets.
"Their goal was to create chaos here," said Hamza. "They thought it would cut the number of fighters that can be sent to Mosul."
As the extent of the attack became apparent, security officials called for reinforcements: up to 3,000 peshmerga were called up from Erbil and Suleimaniya. The U.S. military also carried out air strikes, according to a Western diplomat familiar with the operation.
Even after reinforcements arrived, heavy fighting continued for several hours. The shootout at the Asayesh building only ended at five p.m. on Friday, roughly 14 hours after it began.
Local TV footage showed tracer fire zipping across the sky and smoke rising from the city center on Friday night. Sporadic clashes continued through Saturday and Sunday.
For security officials trying to prevent another attack, the biggest concern is the extent of support within the city for Islamic State.
"There are sleeper cells who cooperated with them," said Hamza. "They have a deep animosity toward Kurds, Shi’ites and the central government."
(This story corrects Zebari's former ministry, paragraph 16)
(Additional reporting by Stephen Kalin and Phil Stewart in Erbil; Editing by Dominic Evans)