LAWS, FALL SHORT: PAGE 2 – A drone carrying a small amount of radioactive cesium that was found on the roof of the prime minister’s office may have landed there in the last few days, investigative sources said Thursday, as authorities moved to beef up security and weighed regulating drone flights.

When Prime Minister Shinzo Abe used the helipad on the roof on March 22 to fly to Kanagawa Prefecture for a graduation ceremony at the National Defense Academy, the four-propeller drone was not there and no staff members had visited the roof since then, the sources said.

The drone, which measures about 50 cm in diameter, was dry when it was found around 10:20 a.m. on Wednesday, suggesting it had landed after April 20 when it rained in Tokyo.

Sources of radiation found on the drone may be from the Fukushima No. 1 nuclear power plant, the investigators said, which experienced three reactor-core meltdowns after the March 2011 tsunami and earthquake, scattering radioactive material across a large swath of eastern Japan.

The rooftop was not regularly checked by security staff, according to the Metropolitan Police Department, which added that staff at the prime minister’s office discovered the drone on the roof Wednesday morning when they were showing new employees around the office.

Investigators continued to analyze footage of surveillance cameras and interview people as they scrambled to find out when the unmanned aircraft landed on the building and who was responsible.

In a related move, the Japan unit of Chinese technology firm DJI, the maker of the drone in question, announced Thursday that it would change how its drones operate. Because the devices are fed with GPS data, no-fly zones can be set by modifying their programs. Areas around airports are already on the list, and the firm said it will now add the prime minister’s office and the Imperial Palace.

Chief Cabinet Secretary Yoshihide Suga told a press conference on Thursday that the government will consider regulating drone flights by creating legislation during the current Diet session.

“We should start from where we can as soon as possible,” the top government spokesman said.

“There is a risk that unmanned aircraft could be used for a terrorist attack at events such as the Olympics or the G-7 summit,” Suga told reporters earlier.

Leaders of the G-7 developed countries are scheduled to meet in Japan next year.

The government will convene a meeting of officials from bodies ranging from the police to the land ministry and industry ministry to examine laws and regulations, he said.

The drone was equipped with what appeared to be a small camera and a smoke flare, and was emblazoned with a radiation symbol. Investigators said they also detected trace amounts of radioactive cesium in a liquid container attached to the device.

The cesium found on the device does not exist in nature, and investigators are looking into the possibility that the radiation from the wrecked Fukushima plant could have been added to the liquid.

“This could potentially lead to more regulations on unmanned aircraft,” said Koichi Nakano, a professor of politics at Sophia University in Tokyo. “Much depends on whether the radioactive material found indicates this was an attack.”

The drone was identified by public broadcaster NHK as a Phantom, an aircraft made by Chinese company SZ DJI Technology Co. — the same type that was flown onto the grounds of the White House in January. After that incident, U.S. President Barack Obama spoke of the need for regulations on the use of small unmanned aircraft by civilians in his country.

At present, Japan regards drones as toys and allows them to fly freely at altitudes of up to 250 meters except near airports.

The government is specifically considering setting up no-fly zones for drones over the prime minister’s office, the Imperial Palace and other important facilities. It is also considering allowing the jamming of radio signals to prevent the control of such devices in the vicinity.

The drone’s discovery on the roof of the prime minister’s office seemed likely to push police to take additional steps beyond the investigation. They had been studying ways to detect unmanned aerial devices approaching important facilities since a drone crashed on the grounds of the White House in January.

On Wednesday, the National Police Agency instructed police departments across the country to enhance the monitoring of airspace above important facilities, such as government buildings, nuclear power plants and airports, police sources said.

The NPA ordered riot police to watch for the approach of drones at such facilities