An American stockpile of some 50 nuclear bombs stored at an airbase in southern Turkey are at risk of being captured by "terrorists or other hostile forces," a U.S. think tank reported on Monday.

Incirlik, located just 110 kilometers (70 miles) from the border with Syria, is a major NATO base and a crucial launching pad for the U.S.-led coalition battling ISIS.

"Whether the U.S. could have maintained control of the weapons in the event of a protracted civil conflict in Turkey is an unanswerable question," said the report by the Stimson Center, a Washington-based nonprofit institution devoted to enhancing international peace, according to AFP.

While critics have long been alarmed about the nuclear stockpile at the base, the aftermath of the failed military coup in Turkey on July 15 has sparked renewed fear.

"From a security point of view, it's a roll of the dice" to keep the nuclear bombs stored at Incirlik, report co-author Laicie Heeley told AFP.

"There are significant safeguards in place... But safeguards are just that, they don't eliminate risk. In the event of a coup, we can't say for certain that we would have been able to maintain control," she said.

Incirlik hosts aircraft from the United States, Germany, Britain, Saudi Arabia and Qatar involved in the U.S.-led air campaign against ISIS. In an interview in July, Turkish Foreign Minister Mevlut Cavusoglu had appeared to suggest Ankara could open up Incirlik to Russia, a move that could raise concern among Turkey's NATO partners already using the base.

Turkey's decision in July 2015 to allow the U.S. to use the base at Incirlik followed a long reluctance by Ankara to become engaged in the fight against Islamist militants.