The Pentagon and US State Department on Tuesday ordered families of US troops and civilian personnel stationed in southern Turkey to leave the region due to security fears.

The order encompasses the city of Adana, where a US consulate and Incirlik air base are located, as well as Ismir and Mugla provinces.

"This decision allows for the deliberate, safe return of family members from these areas due to continued security concerns in the region," the Pentagon said in a statement.

The State Department also restricted official visits to Turkey "mission-critical" travel only.

The Pentagon in September encouraged the families of troops and diplomats stationed in southern Turkey to leave the country, but there was no mandatory order.

In addition to the ordered evacuations of family members, the United States also re-issued a travel warning to all Americans in Turkey.

"The US Department of State warns US citizens of increased threats from terrorist groups throughout Turkey and to avoid travel to southeastern Turkey," the State Department said.

"Foreign and US tourists have been explicitly targeted by international and indigenous terrorist organizations," it added, cautioning Americans to avoid areas close to the Syrian border.

Fears of Islamic State jihadists staging fresh strikes are high following last week's attacks in Brussels.

Incirlik has become a key base for the United States and the coalition it leads against IS fighters in Iraq and Syria.

The strategically located facility provides coalition drones and warplanes fast access to IS targets across northern Syria and into Iraq.

"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," US European Command head General Philip Breedlove said.

Military officials said the order was prompted by "continued security concerns" rather than a specific threat.

In all, 670 dependents of US military personnel -- as well as 287 pets -- were expected to evacuate.

The US consulate in Adana will remain open as usual.