Washington (CNN) As Turkey deals with the fallout of a failed coup, the country's fragility and proximity to Islamic terrorism have raised questions about the safety of US nuclear weapons stationed there.

Most experts believe that the US maintains 50 nuclear weapons in Turkey housed at the US air base at Incirlik. The weapons are Cold War-era B-61 "gravity" bombs.

"It's an open secret" the bombs are at Incirlik, Joshua Walker of the German Marshall Fund, who specializes on US-Turkey relations, told CNN.

Turkish authorities encircled the base, cut off the power supply and temporary closed the airspace around Incirlik as they fought off the coup launched on Friday.

Incirlik, a joint US-Turkish air base, was established in the 1950s in southeastern Turkey. The base has played a critical role in the fight against ISIS, as the US launches strikes into nearby Syria.

While the Pentagon will not publicly confirm the presence of nuclear weapons at Incirlik, US officials are saying all American weapons in Turkey remain safely in US hands.

"We've taken all those steps that we need to take to make sure that everything that we control in Turkey is safe and secure," Pentagon spokesman Peter Cook told reporters Monday.

There is also no indication that US military personnel or technical experts from the Department of Energy went to Turkey to provide further oversight for the weapons or to move them outside of Turkey due to concerns about their security.

But if that were to happen, it would be such a highly classified operation that only a small handful of personnel in addition to the President would know about it, a US official told CNN.

While US aircraft, weapons and personnel at Incirlik are located on a separate portion of the base from where Turkish forces operate, within hours of the attempted coup, the US raised force protection levels for its 2,700 military personnel in Turkey, including Incirlik, to its highest classification. The condition, "Delta," technically indicates an attack is imminent.

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US officials say the raising of the security level had to do with overall security concerns and not the nuclear weapons in particular. However, the upgraded security posture does also provide enhanced security conditions at Incirlik.

Officials noted that the high level of security on the US side of the base could not be kept in place indefinitely without having to bring in more personnel.

But Walker, who served at the US Embassy in Ankara, called any concern about the security of the weapons "hyperbolic," saying that the weapons would still need to be activated from Washington to be usable.

The Cold War-era nuclear weapons are part of NATO's deterrence strategy.

"As long as nuclear weapons exist, NATO will remain a nuclear alliance," reads the official declaration from the July NATO summit in Warsaw, Poland.

"The bombs have been there since the Cold War to counter what at the time was perceived superiority in Soviet conventional forces," Tom Collina, director of policy at the Ploughshares Fund, told CNN.

He noted that the US also stations these types of nuclear weapons in Germany, Italy and the Netherlands.

In Germany, their presence and usefulness have been questioned by leading politicians. German Foreign Minister Frank-Walter Steinmeier told German publication Der Spiegel in 2009 that, "These weapons are militarily obsolete today." He said that he would try to get the bombs "removed from Germany."

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But other members of NATO want to keep the weapons as a political signal of alliance unity.

Walker noted that the bombs "are a point of pride in Turkey," adding that Turkey sees them and the nuclear umbrella they represent as one of the "main benefits of being in NATO."

Decisions about NATO's nuclear weapons have to be made by unanimous vote by all 28 member states.

The US has long had nuclear weapons in Turkey, most notably Jupiter missiles that John F. Kennedy secretly withdrew from the country following the Cuban Missile Crisis of 1962 when the Soviet Union and America climbed down from the brink of a nuclear confrontation.

Collina of the Ploughshares Fund added that this is not the first time concerns have been raised about the security of nuclear weapons in NATO nations.

Turkey had a coup in 1971 and Greece had one in 1967. And Collina noted that when NATO members Turkey and Greece faced off over Cyprus in 1974, the US withdrew its nuclear weapons from Greece and rendered its nukes in Turkey inoperable.