TOKYO (REUTERS) - Japan's government plans to impose a revised roadmap by June on decommissioning reactors at the Fukushima Daiichi plant, putting pressure on the operator to push ahead with an unprecedented project expected to take 30 to 40 years.

The reactors were declared to be in a stable state called cold shutdown in December 2011, nine months after a massive earthquake and tsunami led to meltdowns.

But Tokyo Electric Power Co is struggling to carry out the work in an environment of high radiation levels, and experts say it could cost at least US$100 billion to close the reactors down.

Trade Minister Toshimitsu Motegi said on Thursday the government's newly appointed management group for the decommissioning project would discuss ways to advance the timing of taking fuel out of the reactors.

Among the immediate tasks is dealing with volumes of contaminated water from cooling the reactors, Mr Motegi was also quoted as saying by Masayuki Ono, Tokyo Electric's general manager in charge of nuclear plant sites.

Ono held a news conference after the group, including executives from Tokyo Electric and two Fukushima Daiichi plant suppliers, Hitachi Ltd and Toshiba Corp, ended its first meeting.

Work on treatment and storage of the contaminated water is behind schedule in the company's earlier plan, while the task of removing fuel one of the damaged spent fuel pools is running ahead of a schedule, Mr Ono said.