BEIRUT (Reuters) - Islamic State is building up its defenses in a pocket of territory on the Syrian-Iraqi frontier, the U.S.-led coalition said on Friday, in an anticipation of assaults by Syrian and Iraqi forces aiming to snuff out the jihadists’ last stronghold.

Iraq launched an offensive on Thursday to capture the last Iraqi territory held by Islamic State, the areas of Rawa and al-Qaim, a town just over the border from the Syrian town of Albu Kamal, which is also held by the jihadists.

“Right now, we are seeing the buildup of (IS) defenses in both al-Qaim and in Albu Kamal,” Colonel Ryan Dillon told Reuters by phone, adding that Islamic State’s leadership had shifted to Albu Kamal from towns deeper into Syria.

Albu Kamal is in the crosshairs of both the U.S.-led coalition and the Syrian government and its Iranian-backed militia allies. Pro-Damascus forces, who are also backed by the Russian air force, said on Thursday they would march on the town having driven IS out of a base some 70 km (40 miles) away.

Dillon said Albu Kamal was “definitely” a target for the coalition but said it would be up to the leadership of the coalition’s Syrian allies, the Syrian Democratic Forces (SDF), to take the decision on a ground assault.

The SDF’s priority for now was to shore up its control over the al-Omar oil field, Syria’s largest, which was captured from IS on Sunday, he said.

“Right now, we have to consolidate that area in and around Omar oilfield and the area that led up to it to make sure that that area is secure, and then it’ll be the SDF leadership decision if they can allocate the right resource to adequately push into Albu Kamal,” he said.

Assisted by the coalition, the SDF is fighting IS on the eastern banks of the Euphrates, whereas the Syrian army and its allies, supported by Russian air power, is largely fighting on the western banks of the river.

Dillon said IS fighters were now “much different fighters” from the ones the U.S.-led coalition fought leading up to the battle for Mosul, the Iraqi city recaptured from IS in June.

“We have not seen this fight to the death that we saw in Mosul, and I think it is attributed much to their morale,” he said.