More than 500 Britons in Japan have been given iodine tablets to counteract the effects of radiation leaking from the country's crippled nuclear facility.
The Foreign Office said the tablets, which are used to stop the body absorbing radioactive iodine, have been distributed to around 540 British nationals so far.
The revelation came as police estimates indicated 18,000 people died in the devastating 9.0-magnitude earthquake and tsunami.
Meanwhile, engineers at the stricken Fukushima Dai-ichi nuclear plant managed to restore power to two reactors. But the breakthrough was tempered with the news that pressure had unexpectedly risen at another unit at the plant.
A Foreign Office spokeswoman said the tablets were handed out only to those people who had requested them. She added: "The British Embassy is distributing iodine tablets in Tokyo and Niigata as a contingency measure. People should wait until advised to take the tablets. Iodine tablets have been distributed to around 540 British nationals."
The making safe of two of the six reactors represents the first breakthrough at the Fukushima plant since it was catastrophically damaged when the quake and subsequent tsunami struck on March 11.
Tokyo Electric Power Company said Units 5 and 6 were safe after days of pumping water into the reactors' pool brought temperatures down. But the two units are the least problematic of the six at the site which began overheating after the earthquake-triggered tsunami disrupted the plant's cooling systems.
Engineers reported that pressure had unexpectedly risen in a third unit at the reactor, raising the prospect that plant operators may need to deliberately release radioactive steam to relieve the problem.
As day broke, Japan's military resumed dousing of the complex's troubled Unit 4.
In the wake of the crisis at the plant, anti-nuclear power campaigners held a vigil for those affected by events at Fukushima. About 100 people gathered on Whitehall, near Downing Street, to pay their respects to those who died in the Japanese earthquake and to call for an end to nuclear power.