Andrew Tilghman, Military Times, and John Bacon, USA TODAY

The Pentagon ordered families of hundreds of U.S. military members to evacuate southern Turkey amid growing violence in the country, and on the eve of Turkish President Recep Tayyip Erdoğan's arrival in the U.S. for security meetings.

The "ordered departure" on Tuesday comes two days before Erdoğan meets with Vice President Biden during a nuclear security summit in Washington. White House Press Secretary Josh Earnest said Erdoğan and President Obama will meet informally.

The decision affects almost 700 family members and other U.S. civilians assigned to Incirlik Air Base, a consulate in Adana and smaller facilities in the cities of Izmir and Mugla.

Incirlik Air Base, home to the U.S. 39th Air Base Wing, is a crucial player in the war against the Islamic State. Last year, Turkey agreed to allow use of the base for U.S.-coalition jets conducting airstrikes in Syria and Iraq. NATO's Allied Land Command is based in Izmir.

The mandatory evacuation does not include more than 100 family members based in Ankara and Istanbul despite recent bombings in both cities. A Feb. 17 car bomb in the capital, Ankara, killed at least 30 people, and a suicide bombing March 19 on a popular shopping street in Istanbul killed five people, including two Americans.

On March 9, the Defense Department-run school at Incirlik, less than 100 miles from the Syrian border, was closed due to security concerns, and the base imposed additional protective measures.

Car bomb kills dozens in Turkish capital

The total U.S. military force deployed at Incirlik has grown to nearly 2,500, from about 1,300 last year, after the Turkish government agreed to let U.S. combat aircraft use the base. The base's increasingly prominent role in the fight against the Islamic State group also raised new security concerns. Pentagon Press Secretary Peter Cook said the decision was not triggered by a specific threat.

State Department spokesman John Kirby said Secretary of State John Kerry was involved in the decision and notified Turkish leaders Monday. "This was a decision made out of an abundance of caution to keep people as safe as possible," Kirby said.

Michael Desch, co-director of the University of Notre Dame's International Security Program, said the Pentagon's decision to evacuate families is unsurprising given the region's perilous terror climate.

"The decision was obvious given the series of attacks in Turkey, but I think the final straw was Brussels," Desch said of the terror attacks in Belgium last week that killed more than 30 people. "The risk-management people must have determined that Turkey was low-hanging fruit in terms of vulnerabilities."

In July, worries about extremists targeting U.S. troops and their families prompted military officials to lock down the base and prohibit the roughly 5,000 American troops, civilians and dependents from venturing out to the "American alley" outside the installation's main gate, where troops for years have patronized kabob shops, carpet stores and local markets.

In September, the Defense Department offered voluntary evacuations to about 900 military dependents at Incirlik. About 80 people, or less than 10%, decided to leave, base officials said. The dependents that remain now must leave, the Pentagon said.

Gen. Philip Breedlove, chief of the U.S. European Command, said tthe decision does not foreshadow a permanent end to accompanied tours of duty in the area.

“We understand this is disruptive to our military families, but we must keep them safe and ensure the combat effectiveness of our forces to support our strong ally Turkey in the fight against terrorism," he said.

