The top U.S. military leader said Sunday that Islamic State militants recently came within 15 miles of the Baghdad airport after overrunning Iraqi forces, adding to concerns about whether U.S. airstrikes alone can stop the jihadist army’s foray into Iraq.

Gen. Martin Dempsey, the Joint Chiefs of Staff chairman, told ABC’s “This Week” that Apache helicopters were for the first time called in to stop the extremists’ “straight shot to the airport.”  

“We were not going to allow that to happen,” said Dempsey, acknowledging the risk of using low-flying helicopters instead of fighter jets. “We need that airport.”

However, Dempsey said, there may come a time when he might recommend that American advisers accompany Iraqi troops against Islamic State targets.

Dempsey does not think Baghdad is in imminent jeopardy of being overrun by the Islamic State army but said individual members have infiltrated the surrounding Sunni population, which gives them the capability to fire indirectly into the city.

“We've been successful, mostly the Iraqis have been successful, in keeping (Islamic State) out of range,” Dempsey said. “But I have no doubt there will be days when they use indirect fire into Baghdad.”

Most of the recent attention has focused on the Islamic State, or ISIS, making headway in overtaking the key Syrian border town of Kobani, despite U.S.-led air strikes and efforts by Kurdish ground forces.

Dempsey is scheduled to hold an urgent meeting later this week with roughly 20 other leaders in the coalition against the Islamic State to discuss the group’s advances.

He told ABC that Mosul, in northern Iraq, could at some point be the "decisive" battle in the ground campaign.

Dempsey said the Obama administration has not asked him to help negotiate with Syria a no-fly zone in that country to help coalition air-strike efforts, as Turkey has requested.

But Dempsey said he anticipates circumstances in which such a zone “would be part of the campaign.”

Meanwhile, National Security Adviser Susan Rice said the U.S. was not reassessing its strategy and steadfastly held to President Obama’s position that he will not send ground troops to the Middle East to “degrade and destroy” the Islamic State.

“We are in the early stages as what President Obama said is a long-term effort,” Rice told NBC’s “Meet the Press.” “This is going to take time. …  It cannot be judged by what happens in one particular time or town.”

She also repeated the U.S. strategy is to build up the Iraqi army and support the efforts of the “moderate opposition” to the Syrian regime that is also trying to defeat ISIS.

Rice said the airstrikes are “off to a strong start” but acknowledged that effort will also take time.

The Associated Press contributed to this report.