Washington: An uptick in air strikes in northern Iraq this past week marks the beginning of a broader effort to disrupt Daesh supply lines ahead of an expected operation later this year to take back the city from militants, US military officials said Friday.

Coalition air strikes have pounded at least two dozen locations around Mosul, destroying dozens of vehicles, buildings, fighting positions and insurgent units.

The air strikes, said one senior military official, are the start of a new phase, and military leaders are watching to see how air strikes militants respond as their supply and communications lines dry up. The official was not authorized to discuss the operations publicly so spoke on condition of anonymity.

Meanwhile, at the Pentagon Friday Rear Adm. John Kirby said US efforts to train Iraqi forces and moderate Syrian rebels to fight Daesh militants are moving forward, even as insurgents still control about 21,000 square miles of Iraq.

Kirby, the Pentagon press secretary, laid out a flurry of details and data aimed at showing the progress the coalition has made since it began air strikes against the insurgents in Iraq last August.

Kirby said that about 270 square miles in Iraq have been regained from militants, mostly by Kurdish forces in the north. He cautioned that control of land across the country will continually change over time, and it will be a long struggle.

“I think we all recognize that it’s a small percentage of the total right now. But we’re only six, seven months into this thing, too,” said Kirby. “ISIL (Daesh) had a big head start on us, coming into the summer. A pretty aggressive first quarter for those guys.”

He added, however, that while it will take time to uproot Daesh, 270 square miles also is not an insignificant amount.

US officials have said the coalition has stalled the momentum of the Daesh militants, and Kirby said Friday that about 6,000 of the fighters have been killed, according to estimated battle damage assessment of the air strikes. US officials estimate there were between 20,000 and about 30,000 insurgent fighters, including core Daesh militants and other aligned militias.

Kirby said the number killed is “not a metric that we’re going to hang our hat on when it comes to talking to the success of this strategy ... This is not a uniformed army with identification cards and recruiting posters. So, it’s hard to say at any given time how many fighters they have in the field.”

Instead, he said that more relevant measures of success would be the effect air strikes and other operations have had on the insurgents’ ability to operate and communicate. He said Daesh is more on the defensive, struggling to get supplies and financing and having difficulties replacing destroyed weapons and machinery.

“While we’re seeing all that, we’re also mindful that they’re still a potent force inside Iraq and in Syria. And that this is going to continue to take some time,” he said.

Kirby also said that training has begun in all four planned sites in Iraq. About 3,600 Iraqi and Kurdish forces are in the pipeline for training at sites in Irbil, Bismayah, Taji and at Anbar Province’s Al Asad Air Base. The training camp in Arbil began operations Friday, and about 100 peshmerga fighters have started their instruction.

So far, plans are to train nine Iraqi brigades and three Kurdish brigades.

Training for the moderate Syrian rebels has also begun to move forward. Kirby said Friday that an advance team of fewer than 100 US troops will soon head to training sites in Saudi Arabia, Turkey and Qatar to begin site surveys and other preparations for the Syrian rebel training. The next wave of several hundred trainers and support troops could deploy in the coming weeks.

Preliminary discussions with Syrian rebel groups have started, but actual vetting of individual fighters for the training hasn’t begun yet. Kirby said military leaders are optimistic that they will have an adequate pool of rebel fighters, adding that they will be vetted periodically throughout the process to insure they are working with the right people.

The recruiting process is expected to take three to five months, so training could begin by early spring. That training will take six to eight months, so the first Syrian fighters won’t be on the battlefield until late fall or the end of the year.