Image copyright AFP Image caption Harumafuji has publicly apologized for the assault

Former sumo grand champion Harumafuji has been charged with assaulting a junior wrestler in a scandal that has rocked Japan's ceremonial sport.

The 33-year-old wrestler from Mongolia has already apologised and stepped down over the incident.

He is facing a summary indictment, which means he is expected to be fined rather than tried in court.

Japan's sumo world has been hit by scandals involving violence, mafia links and match fixing in recent years.

Harumafuji's assault on fellow Mongolian Takanoiwa happened while they were out drinking with other wrestlers in a bar in the western city of Tottori in October.

The grand champion is reported to have been angered that his countryman was checking his phone while being given advice. The latter was admitted to hospital with concussion and a fractured skull.

Harumafuji admitted punching him hitting him with a karaoke remote control but denied using a beer bottle in the attack.

"I'm truly sorry for hurting Takanoiwa mentally and physically," Harumafuji told police, according to Jiji Press.

Harumafuji started his career in Japan at the age of 16 and was promoted to grand champion or yokozuna - sumo's highest rank - in 2012.

The Japan Sumo Association (JSA) also recommended that its director Takanohana be demoted for failing to report the incident quickly enough, Kyodo news agency said.

Takanohana is a former sumo champion himself and the JSA is expected to finalise its decision in early January, according to Kyodo.

What is sumo?

Japan's much-loved traditional sport dates back hundreds of years

Two wrestlers face off in an elevated circular ring and try to push each other to the ground or out of the ring

There are six tournaments each year in which each wrestler fights 15 bouts

Wrestlers, who traditionally go by one fighting name, are ranked and the ultimate goal is to become a yokozuna (grand champion)

How does sumo wrestling work?

The incident around Harumafuji follows a string of scandals in recent years.

Last year, a wrestler and his coach had to pay nearly $300,000 (£230,000) to a fellow fighter they allegedly abused so badly he lost sight in one eye, according to reports.

Several wrestlers have also been implicated in match fixing scandals and links between sumo and the mafia-like yakuza crime syndicates.

Another Mongolian grand champion retired from the sport in 2010 after reports of his involvement in a drunken brawl.

In 2007 a sumo stable-master received six years in prison after a novice was beaten to death by older wrestlers.