By the end of the day, the department will have "completed over four dozen flights," the official said on condition of anonymity.

"We have directly provided security guidance and travel assistance to about 32,000 impacted Americans," the official added.

Countries worldwide have urged citizens to avoid the Middle East during the ongoing war against Iran, which has seen violence erupt across much of the region.

But closed airspace and airports meant thousands of people were struggling to find a way out, and flights have only partially resumed in recent days.

US officials in particular came under fire for allegedly not giving citizens sufficient warning to avoid the Middle East in the days before launching the attacks on Iran.

In recent days the government has scrambled to organize charter flights, using emergency funds so that travellers can fly without cost -- an unusual perk in such circumstances.

"We have offered departure options to nearly every American in the region who has asked us for assistance," the state department official said.

"Most Americans who requested assistance have declined seats when offered, opting either to remain in (the) country or book commercial flight options which offer greater flexibility in terms of destination and luggage."

Separately on Thursday, the state department raised its terror advisory alert on Azerbaijan to Level 3 (Reconsider Travel), citing "terrorism, armed conflict, and risk of landmines."

Azerbaijan has been the target of what it says are Iranian drone strikes since the fighting broke out, a charge Tehran has denied.