Japan has hanged a man who robbed and killed a woman after plotting the crime with accomplices online, in the first execution to be carried out by the country this year.

Thursday's hanging brings to 12 the total number of death sentences carried out since Prime Minister Shinzo Abe took power in 2012.

Tsukasa Kanda, 44, was executed for the murder of 31-year-old Rie Isogai in Nagoya, central Japan, in 2007.

Kanda met two accomplices via a mobile phone-based web service and the three of them devised a plan to target a random woman victim.

The men kidnapped Isogai from a Nagoya street and suffocated her by wrapping her head and neck with a plastic bag, adhesive tape and rope, before battering her head with a hammer, according to justice ministry records.

Kanda's accomplices are serving life sentences.

Questioning the death penalty in Japan

"This was an extremely brutal case that brought unimaginable suffering to the victim and her family," Justice Minister Yoko Kamikawa told a press briefing after the execution, the first since she came to office in October last year.

"After a series of careful reviews, I ordered the execution," she said.

Rights group Amnesty International on Thursday accused the country of attempting to avoid public scrutiny by carrying out the execution while national political and media attention was focused on the government's plans to extend its military capacities.

International advocacy groups say Japan's system is also cruel because inmates can wait for their executions for many years in solitary confinement and are only told of their impending death a few hours ahead of time.

Kanda did not appeal his death sentence after the original district court ruling.