KUALA LUMPUR (Reuters) - Malaysian democracy group Bersih plans a protest rally to demand greater government accountability and action to tackle a multi-billion-dollar scandal at state fund 1MDB, an official of the group said on Wednesday.

The U.S. Justice Department filed civil lawsuits last month alleging that more than $3.5 billion was misappropriated from state fund 1MDB, founded by Prime Minister Najib Razak and whose advisory council he chaired until recently.

Bersih said it planned a roadshow and several protests ahead of the street demonstration, whose timing it did not reveal.

"Not protesting is not an option," Bersih chairwoman Maria Chin told reporters, adding that the group aimed to gather more diverse groups and stakeholders for the rally, although she did not identify them.

"Awareness of 1MDB at the ground level is not yet there, we need to raise the level of anger and awareness," she added.

More than 200,000 people turned out in the Malaysian capital last August for a similar rally organized by Bersih, demanding the resignation of Najib.

Opponents of Bersih, which draws the bulk of its support from Malaysia's ethnic Chinese minority, said at the time that the protest aimed to challenge the political power of ethnic majority Malays.

A national security measure took effect this week in the middle-income emerging country, giving the prime minister power to suspend civil liberties in any region he declares a "security area".

The U.S. civil lawsuits do not name Najib, but refer to a high-ranking government official who received more than $700 million of the misappropriated funds.

A source familiar with the investigations told Reuters the official, named as Malaysian Official 1 in the lawsuits, was Najib.

Najib, who has denied any wrongdoing, has said Malaysia will cooperate in international investigations of the One Malaysia Development Berhad (1MDB) case.

(Reporting by Joseph Sipalan; Editing by Clarence Fernandez)