Pirates wielding rocket-propelled grenades and AK-47s have prompted Japan to ease a ban on civilians carrying guns, allowing guards on locally registered oil tankers to be armed for the first time.

Shipping companies will be able to place security personnel with guns on the tankers when sailing through specified areas of the Indian Ocean and in and around the Gulf of Aden, where pirates have collected hundreds of millions of dollars by hijacking ships. The change in the law, which became effective Nov. 30 and only applies to oil tankers, marks the first time Japan has authorized civilians to carry automatic weapons.

The change will allow an extra level of safety for the tankers, which are already protected by Japanese escort ships and patrol aircraft on routes to the Middle East. Kawasaki Kisen Kaisha Ltd., Japan's third-largest shipping line, aims to put armed guards provided by a U.K. company on locally registered tankers as early as this month, said Osamu Tanetani, a manager at the Tokyo-based company's marine safety team.

"Japan has finally caught up with the international norm," said Seijiro Morimoto, a researcher at the Japan Maritime Center, which advocated early adoption of the system. "Combining the efforts of naval operations with private security guards is the most effective way to deter piracy."

Civilians in Japan have been barred from carrying guns, except for hunting weapons, under laws dating back to 1588, said Isami Takeda, professor of international relations in the faculty of foreign studies at Dokkyo University in Soka, Saitama Prefecture.

Japanese tankers registered overseas were already able to carry armed guards. Kawasaki Kisen, based in Tokyo, uses armed security personnel from a British company on its overseas-registered ships.