WASHINGTON (AFP) – The US State Department said Monday it is making potassium iodide (KI) available to US government workers and their dependents located in the vicinity of a troubled Japanese nuclear plant.

"The US government is making available potassium iodide as a precautionary measure for United States government personnel and dependents" in Nagoya, Tokyo, Yokohama and 15 prefectures "out of an abundance of caution," the department said in a travel warning.

It said iodide should be consumed only after specific instruction from the the government.

"While there is no indication that it will become advisable to take KI, out of an abundance of caution the United States government is making it available to its personnel and family members to be used only upon direction if a change in circumstances were to warrant," the warning said.

It added that no one should take KI at this time.

Earlier on Monday, the situation at Fukushima nuclear -- which the Japanese government had said was making "slow but steady progress" following this month's devastating earthquake and tsunami -- appeared to suffer a new setback again when smoke arose from one of the reactors, forcing authorities to evacuate workers.

At 3:55 pm (0655 GMT), a "light grey plume of smoke" rose from reactor number three, according to a local spokesman.

"Due to this problem, the operator temporarily pulled out the workers, while checking on the condition of the site," the spokesman said.