The Pentagon warned Wednesday US air power on its own could not prevent Islamic State jihadists from capturing the Syrian border town of Kobane, even as US warplanes kept up bombing raids in the area.

US-led aircraft were hitting the IS group at every opportunity but without a competent force on the ground to work with, there were limits to what could be accomplished by bombing from the air, spokesman Rear Admiral John Kirby told reporters.

Smoke billows from the South west of the Syrian border town of Kobane also known as Ain Al-Arab

“Air strikes alone are not going to do this, not going to fix this, not going to save the town of Kobane,” Kirby said.

“We know that. And we’ve been saying that over and over again.”

Ultimately, “capable” ground forces — rebel fighters in Syria and Iraqi government troops — would have to defeat the IS group, but that would take time, he said.

Kirby said that “we don’t have a willing, capable, effective partner on the ground inside Syria right now. It’s just a fact.”

Other towns could also fall to the IS group until local ground forces could find their footing, he added.

an F/A-18E Super Hornets attached to the Tomcatters of Strike Fighter Squadron (VFA) 31 on the flight deck of the aircraft carrier USS George H.W. Bush (CVN 77)on August 1, 2014 in the Gulf.

The Pentagon’s sober assessment came after American-led forces carried out six air raids near Kobane on Tuesday and Wednesday in an attempt to help Kurdish militia who have fought a desperate battle to hold off the IS group’s push.

IS extremists have been closing in on Kobane for days but Kurdish forces — backed by US-led air power — reportedly managed to roll back IS militants out of several neighborhoods amid heavy fighting overnight.

The chairman of the US Joint Chiefs of Staff, General Martin Dempsey, said coalition aircraft were bombing the IS group whenever possible but tracking the militants presented a challenge.

“We have been striking when we can,” Dempsey told ABC News in an interview.

IS fighters are “a learning enemy and they know how to maneuver and how to use populations and concealment,” the general said.

He indicated the IS extremists were more difficult to track as they were staying off of mobile phones or other devices that could be monitored.

“They’re becoming more savvy with the use of electronic devices,” he said.

“They don’t fly flags and move around in large convoys the way they did. . . They don’t establish headquarters that are visible or identifiable.”

– Trying to halt IS momentum –

Washington’s air campaign, launched in Iraq on August 8 and extended into Syria on September 23, was designed to halt the advance of the IS group to buy time to build up “moderate” rebel forces in Syria and Baghdad government and Kurdish troops in Iraq.

But despite the bombing raids, the IS jihadists have continued to gain ground in both countries, including around the key town of Kobane near the Turkish border.