U.S. officials in Japan will pay for the voluntary departure of any family members of diplomat at several locations in the country, amid growing concerns about radiation from a troubled nuclear plant in Fukushima, Japan.

Under Secretary of State Patrick Kennedy told reporters in a Wednesday conference call that the situation at the plant had not reached a point where an ordered departure was needed for family members or U.S. government employees.

And this is, in fact, the lowest step on our hierarchy, he said of the latest measure.

The U.S. embassy in Tokyo announced support a voluntary departure of about 600 State Department  family members and dependents of diplomats at three locations.

The voluntary departure has been approved for family members at the American embassy in Tokyo, the U.S. Consulate in Nagoya just west of Tokyo, and the State Department's Foreign Service Institute which has a language training school in Yokohama, according to Under Secretary of State Patrick Kennedy. Not included on that list are Osaka or Sapporo in the north, he said.

[L]et me just emphasize this is voluntary authorized. We have not ordered them to leave ... we have made this opportunity available to them should they choose to exercise it, he said in a conference call with reporters on Wednesday.

He said arrangements were being made to bring some chartered aircraft into Tokyo for both U.S. government family members who had chose to leave or for an American citizens who might need assistance. Consular officers will be walking through the terminals at Haneda and Narita airports looking for U.S. citizens who have been unable to make a reservation on a commercial flight leaving the country, he said.

He said the planes would be going to other major airports in the region.

The latest measure comes as the embassy in Tokyo has already recommended the evacuation of American citizens to at least 50 miles from the Fukushima Daiichi nuclear plant on the eastern coast of the country, several hundred miles northeast of Tokyo. That is part of a travel warning the State Department issued Wednesday.

In the travel warning, the State Department said it strongly urges U.S. citizens to defer travel to Japan at this time and those in Japan should consider departing.