Prosecutors on Monday sought an 18-month prison term for a Japanese journalist on charges of defaming President Park Geun-hye in an article he wrote in August 2014.

Tatsuya Kato, a 49-year-old former Seoul bureau chief for the Sankei Shimbun newspaper, is on trial at the Seoul Central District Court.

The trial started last November after Kato was indicted without arrest a month earlier for writing the article in which he cited South Korean news reports concerning Park's suspected relationship with a man.

Picking up rumors in the South Korean daily Chosun Ilbo and the financial industry, he wrote that Park was absent for several hours while meeting with a former male aide when the Sewol ferry sank in April last year, killing more than 300 passengers, mostly teenagers on a school trip.

The government under Park had come under a storm of public criticism for its botched rescue operations in the early hours of the nation's worst maritime disaster.

As Kato's case came to light, critics also raised concerns about the South Korean government's effort to stifle freedom of the press.

Kato's lawyers have argued that the article was not defamatory. But after the presiding judge said during a hearing in March this year that the rumors were false, the Sankei Shimbun ran a note by Kato that he does not intend to argue this point.

The court is set to hand down its ruling Nov. 26.

"In light of freedom of the press and expression, as well as Japan-South Korean relations, we have repeatedly conveyed our concern and strongly called for appropriate responses from the South Korean government," Chief Cabinet Secretary Yoshihide Suga said at a news conference Tuesday.

"But the trial was concluded and prosecutors sought a jail term without the situation improving," he said. "It is extremely regrettable."