The United States is moving toward permanently banning families from accompanying U.S. military and civilian personnel in Turkey, reflecting worsening security conditions there, two U.S. defense sources said on Wednesday.

The Obama administration in March ordered the families of U.S. military and diplomatic personnel to leave Incirlik Air Base, which has been used heavily in the fight against Islamic State group militants, and other parts of southern Turkey.

The move affected about 670 dependents of U.S. military personnel in southern Turkey, but 100 of them in Istanbul and Ankara were allowed to stay.

Now, military officials plan to designate deployments by all U.S. military and civilian personnel to Incirlik base in Adana and other sites in Turkey as “unaccompanied” tours, the sources told Reuters.

The move was under consideration before Tuesday’s suicide bomb attacks at Istanbul’s main airport, which killed 41 people and wounded 239 others, the sources said.

“The change reflects the continued deterioration of security conditions throughout Turkey,” said one of the sources, who was not authorized to speak publicly.

The U.S. military has about 2,200 service members and civilian employees in Turkey, with about 1,500 of those posted to Incirlik base.

The change would not apply to U.S. personnel who are part of a “chief of mission” role or security cooperation team, the sources said.

The 100 dependents of U.S. personnel still in Turkey would be allowed to stay once the new rules took effect, and would depart through natural attrition, said one of the sources.

The State Department on Tuesday warned U.S. citizens of increased threats from militant groups throughout Turkey, and urged them to avoid traveling to the southeastern part of the country.