A group of three Nigerians and a Cameroonian were arrested Tuesday for allegedly scamming several people in Japan out of large amounts of money by feigning romantic interest in them online, police said.

The men are alleged to have targeted the victims last year via social media pretending among other things to be foreign military servicemen needing money, the police said.

The men are also suspected of sending messages saying they wanted to meet their victims and needed financial support, such as to pay for an airline ticket to visit Japan or to leave the military.

According to the police, the men are suspected of having contacted three people between March and June 2018, swindling them out of between 170,000 yen ($1,550) and 6.6 million yen.

They approached a 59-year-old part-time female worker living in the southwestern Japan prefecture of Fukuoka and a 58-year-old female public servant in Hokkaido, pretending to be a U.S. military man who needed money to leave the service, and a doctor living in Syria.

One of the victims was a 46-year-old male office worker from Tokyo who was cheated out of more than 2 million yen believing that he was sending it to an American widow who needed help transferring an "inheritance" to him.

Investigators searched a building in Yoshikawa, Saitama Prefecture, which is suspected of being the group's headquarters, according to investigative sources.

The group is believed to be active in eastern Japan prefectures, and a man suspected of being the group's leader lives in Chiba Prefecture east of Tokyo, the sources said.

Such "international romance" scams are on the rise in Japan, and scammers use various techniques to lure their victims. According to a non-profit foundation set up to tackle the issue in the wake of an increase in Japanese victims, scammers use various online sites from dating sites to online language sites, emotionally manipulating their targets to make them feel loved, such as with promises of marriage.

The timing of financial requests varies from a few days to more than a year, as the con artists develop a relationship with their victims, gaining their trust.

The requests are initially for small amounts of money, becoming larger later.

Scammers come up with various excuses in asking victims to transfer cash to third person accounts or use international money transfer services. These include illnesses, accidents, or the prospect of a lucrative business contract which needs seed money.

They pretend to be U.S. servicemen in active military theaters such as Syria or Afghanistan, professionals such as engineers or business owners, or female models.

They rarely show their faces online but use photos they find online of men who are unrelated to the scam.

Although the culprits promise to pay their victims back, they never do. There is very little recourse to retrieve any money, warns the foundation.