Police in Nigeria, Ghana and Kenya have arrested dozens of people suspected of carrying out large-scale money-transfer scams.
The scams involve tricking victims into wiring money to bank accounts controlled by fraudsters.
More than 250 people were arrested in 10 countries. Police also conducted raids in the US, UK, Turkey, France, Italy, Japan and Malaysia.
Of those arrested, 167 were from Nigeria.
The FBI coordinated the raids over a period of several months. They targeted groups of people suspected of stealing millions of pounds from companies and individuals.
Almost $3.7m (£3m) in cash was seized during the raids. Evidence gathered from the operation should also lead to another $118m being seized, the FBI said.
Ibrahim Magu, who chairs Nigeria’s Economic and Financial Crimes Commission, told the TodayNG news website that the action was part of a larger effort against groups of suspected tech-savvy criminals called Yahoo boys.
Mr Magu said the raids had led to the seizure of “exotic cars [and] plots of land in choice areas in Lagos and a property in Abuja”.
The FBI has urged anyone handling money transfer requests that arrive by email to take extra time to verify the identity of the sender.