The Kurdish capture of a Syrian military base and nearby territory held by ISIS in recent days is putting renewed focus on the expanding ground fight against the terror network.

Kurdish advances in Syria against ISIS show the terror group is increasingly on the defensive, experts tell FoxNews.com.

“The Kurds have shown themselves more able than we were expecting to conduct offense. We’ve always known the Kurds could defend Kurdish territory particularly well, but the capture of [the air base] is a positive sign that they can move forward,” said Andrew Peek, a former U.S. Army intelligence officer.

The jihadist group has suffered a series of defeats to Kurdish forces since being forced to withdraw from the town of Kobane in January.

“The Kurds have been advancing significantly in recent weeks – they are a well-trained, highly motivated fighting force,” said Nile Gardiner, director of the Heritage Foundation’s Margaret Thatcher Center for Freedom. He believes recent gains on the battlefield will “increase the pressure on the Obama administration to send more support to the Kurdish allies, especially the arms needed in order to gain further ground inside Syria.”

Experts debate whether any momentum building against ISIS could put the group's headquarters in Raqqa at risk for a ground assault. Since September 2014, U.S.-led coalition airstrikes have reached nearly 1,800,with many focused on Raqqa.

“Airstrikes are only a limited means of warfare -- eventually you are going to need, I believe, a U.S. ground presence in order to defeat ISIS,” said Gardiner. “Airstrikes are very limited in their capacity … in order to stave off the ISIS threat; we have to have a strategy for victory, not containment.”

While ISIS remains the top threat, there are concerns a further unraveling of the security situation in Syria could prompt Iran’s involvement.

“There is a real danger for some sort of large-scale Iranian intervention to prop up the Assad regime at the same time as the Kurds are making progress against ISIS; so a war on several fronts,” said Gardiner.

Peek, a Middle Eastern affairs fellow with the American Foreign Policy Council believes Iranian-backed Shiite militias in Iraq could seek a greater say in Syria. “In the absence of U.S. ground troops, they are kind of the only reliable ground forces we have or are fighting ISIS on our behalf.”

Chris Snyder is a producer for FoxNews.com based in New York. Follow him on twitter: @ChrisSnyderFox