Japanese Prime Minister Shinzo Abe on Monday defended as "necessary" an unpopular secrets law that he rushed through parliament, as a new poll showed his support rating had plunged 10 percent in a month.

The conservative hawk admitted he could have better explained the new law, but insisted that it was a vital step to protect Japan and bring it into line with its allies.

"Unless our country establishes rules to manage confidential information, we cannot obtain such information from other countries," he told reporters.

"In order to protect people's lives and property, it was necessary to pass the special secrecy law as quickly as possible."

But journalists, lawyers, academics and rights groups has said the law is illiberal and represents "the largest threat to democracy in postwar Japan."

They claim it undermines press freedoms and the public's right to know.

Last week, a couple of demonstrations in Tokyo attracted upwards of 3,000 people in protest at the legislation.

A survey published by Kyodo News on Monday showed his once-comfortable personal approval rating had dropped 10.3 percent to 47.6 percent since the last poll in November.

A poll by national broadcaster NHK showed a similar drop since last month.

AFP