Prosecutors said on Tuesday they are seeking a sentence of 18 months in prison for two former executives of Mitsubishi Hitachi Power Systems Inc. for allegedly bribing a Thai official over a power plant project, in a case that became well known for being the country's first to involve a plea bargain deal.

Fuyuhiko Nishikida, 63, and Yoshiki Tsuji, 57, were indicted for allegedly conspiring with a senior company executive to pay 11 million baht ($345,000) in February 2015 to a senior official of the Thai Transport Ministry. It is believed the men were hoping to secure favorable treatment in the delivery of power plant cargo to a local port.

Both admitted to the charges during their first hearing at the Tokyo District Court in December. The ruling will be handed down March 1.

"The crime was organized and (the two officials) lacked compliance awareness. Both defendants bear responsibility for playing decisive roles," a prosecutor said in a closing statement.

Their lawyers claimed that they had no choice but to meet the Thai official's request for a bribe and pleaded for leniency as they received no personal gain.

"They regret what they did," one of their lawyers said.

Satoshi Uchida, 64 — the senior executive who was then managing the power plant project — has denied the charges and is on trial in separate court proceedings.

Last year, the Tokyo District Court offered the plea deal between prosecutors and Mitsubishi Hitachi Power, exempting it from an indictment in exchange for the firm's cooperation in the executives' trial.

A whistleblower alerted the company of the bribery in March 2015. The firm reported it to the Tokyo District Public Prosecutor's Office following an internal probe.