Japan has joined an international convention for tackling transnational organized crime after putting into force a law penalizing the planning of a range of crimes.

Tokyo submitted to the United Nations in New York an instrument of acceptance of the U.N. Convention against Transnational Organized Crime, becoming the 188th signatory. Japan is the only country in the Group of Seven that has yet to ratify the convention, despite having signed it in 2000.

The move on Tuesday came after the controversial conspiracy law took effect earlier in the day. The government insists it will help thwart terrorism while critics say the enhanced police power could lead to the suppression of civil liberties.

Prime Minister Shinzo Abe's government has framed the law as an essential tool for tackling terrorism in the run-up to the 2020 Tokyo Olympics, saying it was necessary to ratify the treaty.

But opponents, including legal experts, have warned that the definition of terrorist groups and other organized criminal groups is vague, leaving room for anyone to be punished.

The U.N. convention calls on member countries to legislate a ban on organized crime and money laundering, and to cooperate in probes and on the extradition of suspects.