MANILA, Jan 5, 2013 (AFP) - A Philippine woman and her son have been arrested along with three other local suspects for the gun-for-hire murder of her Japanese husband, police said Saturday.

Hideo Niikura was shot dead by a motorcycle-riding gunman in Dasmarinas, a town about 35 kilometres (22 miles) south of Manila on December 29, a police statement said.

His wife Merlinda Soria, 46, confessed she and an adult son by another man had plotted the killing, the statement said.

The son and one of his friends paid a third man 100,000 pesos (just under $2,500) to commit the murder, according to the statement, which added that the son's friend also corroborated the woman's deposition after their arrest.

Police said the four were detained in separate police raids in Dasmarinas on Friday, along with another male suspect also implicated in the conspiracy.

Police seized two semi-automatic pistols from the alleged gunman and the woman's son, it said.

The statement said mother and son plotted to have her husband killed "over money matters and alleged physical abuses", but did not elaborate.

Local police sources said the couple met in Manila around 1990, got married seven years ago and have a five-year-old child.

The husband decided to permanently relocate to Dasmarinas in September last year, they said.

The victim's home town was not stated in the report.

Japanese embassy officials were unavailable for comment on Saturday.