The deepening U.S. military involvement against Islamic State terrorists in northern Syria indicates the Pentagon will likely send even more troops in coming weeks. Their mission won’t be to fight on the front lines but to bolster Syrian Arab and Kurdish forces in a coming battle for the key city of Raqqa.

On Wednesday, the Pentagon disclosed that Marine pilots airlifted scores of Syrian partner forces to the front lines, kicking off an offensive designed to capture a strategic crossroad along the Euphrates River. It was the first such U.S. assistance to the Arab and Kurdish fighters comprising the Syrian Democratic Forces. In a support role, the U.S. also fired artillery and flew Apache attack helicopters for the first time in Syria.

U.S. officials reported no major developments on the ground Thursday. Resistance from Islamic State fighters appeared less fierce than anticipated, said one official, who wasn’t authorized to publicly discuss an ongoing operation and demanded anonymity. The U.S.-backed forces said in a statement they had already secured some territory.

“It has become a military base to launch our operations on the west bank of the river until eventually liberating all the countryside of Raqqa,” the statement said. Raqqa is the Syrian city that IS has called the capital of its self-declared caliphate. Tabqa lies 45 kilometers, or about 28 miles, west of the city.

The U.S. troops haven’t engaged in ground combat. But the new offensive suggests the Trump administration is taking an increasingly aggressive approach as it plans an assault on Raqqa.

But the moves on Tabqa Dam, as well as the town by the same name and a nearby airfield, also highlight an unresolved U.S. dispute with Turkey over which Syrian forces should participate in the operation to recapture Raqqa.

Turkey, a longstanding U.S. ally in NATO, strongly opposes the Kurdish role because Ankara considers the main Kurdish fighting force, known as YPG, a terrorist organization. Washington, however, sees the YPG as an effective battlefield partner. As recently as this week, U.S. officials said some Kurds would inevitably be part of the Raqqa offensive, although the Pentagon was still holding out hope of reaching an accommodation with the Turks.

Col. Joseph Scrocca, a spokesman for the U.S.-led military coalition that is fighting IS in Syria and Iraq, told reporters at the Pentagon on Wednesday that the Tabqa operation was large and likely would last for weeks. He would not say how many U.S.-allied fighters are involved.

By design, the operation coincides with a potentially climactic battle for Mosul, the main Islamic State group stronghold in Iraq. Together, the battles reflect a U.S. strategy of presenting IS with multiple challenges simultaneously. Although Mosul and Raqqa are easily the two most important IS holdings, their recapture by U.S.-backed local forces is not expected to mark the complete collapse of IS as an international threat.

After taking office, President Donald Trump instructed Defense Secretary Jim Mattis to coordinate a new counter-IS strategy. As a presidential candidate, Trump had promised to quickly defeat the group, saying at one point during the campaign that he had a secret plan.

At a Senate hearing Wednesday, Mattis said the strategy was still in “skeleton” form.

“We’re fleshing it out,” he declared, saying it would include economic, diplomatic, military and covert efforts.

Mattis and other officials have strongly suggested the plan will preserve the central feature of the Obama administration’s approach: Advising and enabling local forces to fight rather than doing it for them.

But as IS loses strength and territory in Iraq and Syria, the U.S. is likely to bolster its support and send some additional troops. Officials have said the new deployment of U.S. forces would probably be small, however.

The U.S. currently has about 1,000 troops in Syria. It has at least 7,000 in Iraq.

(AP)