(CNN) Three Iraqi soldiers were killed and 17 wounded Friday when ISIS militants, driving 10 vehicles packed with explosives, attacked an Iraqi army base near Ramadi.

The head of the Anbar Provincial Council, Sabah Al-Karhut, told CNN the attacks happened in quick succession. He said the 10 vehicles targeted the Iraqi army's 10th Division base northeast of Ramadi.

Even though Iraqi forces have managed to drive ISIS jihadists out of the center of Ramadi , local tribal leaders said this week that ISIS still controls as much as 25% of the city, and significant pockets of ISIS resistance remain.

Still, Prime Minister Haider al-Abadi visited the bombed-out city this week, raising the Iraqi flag and declaring that 2016 "will be the year we drive ISIS out of Iraq."

The Sunni extremist group seized the provincial capital in May. It was a humiliating setback for the Iraqi government and the U.S.-led coalition backing Iraqi forces.

Efforts to expel ISIS are expected to take weeks, especially in light of the jihadists' tactics of hiding among local populations and booby-trapping territory they abandon.

Suicide bombing kills police officers in Tikrit

Attacks by ISIS were not limited to the Ramadi area. On Sunday, ISIS attempted to carry out a coordinated attack on Camp Speicher near eastern Tikrit, Iraqi security officials told CNN.

Camp Speicher, which was a U.S. base for nearly a decade, is where ISIS committed a June 2014 massacre, claiming to have executed hundreds of recruits and soldiers captured outside the camp.

On Sunday, six suicide bombers tried to storm the camp, but, Iraqi police forces opened fire and killed three of them, the officials said. The other three suicide bombers managed to blow themselves up at the main gate of the camp, killing nine police officers. Seven other police officers were wounded.

Taking Mosul will be tough

Iraq's leaders may have their eyes on Mosul as the next prize, but a U.S. military expert said Saturday that taking it will be challenging.

The country's second-largest city, with more than 1 million people, Mosul is about 250 miles north of Baghdad. It fell to ISIS in June 2014 after Iraqi forces fled en masse. The shocking defeat brought the Islamic militant group's military prowess to the fore.

Retired U.S. Army Lt. Gen. Mark Hertling, a CNN military analyst, said he is concerned that the Iraqi government might be trying to accomplish too much too quickly.

"The road to Mosul is going to be long and difficult," he told CNN. "There's got to be a lot of other bases taken for the Iraqi security forces to go north."

Engage with local leaders

The Iraqi government will have to do a lot more to engage the diverse leadership in the north, Hertling said.

"Where you had Sunnis almost exclusively in Ramadi, you've got an interesting mix of Sunnis, some Shia, a lot of Kurds, Some Chaldeans and Syrians; a bunch of different sects and tribes in the northern provinces."

Before Iraqi forces can push north, Hertling said, Abadi's government "has to coordinate with those tribes."

"That's going to take some time. It's ambitious to say they're going to take Mosul in 2016."

A reason for some optimism

But there is reason to be cautiously optimistic, Hertling said.

"If the Iraqi government can come together to support the security forces, which they are doing now, with pay, much better leadership and with support of both the government and the people, we are and will continue to see a turning of the tide.

"You're seeing them taking pride again in being Iraqis, in coming together as a nationalistic force."

He cautioned, "We shouldn't spike the ball just yet in Iraq, but it seems in the latter part of 2015 and the early stages of 2016, we may see some hope yet in the Iraqi security forces and their government.