Online scammers are posing as US serviceman posted overseas and promising love and marriage to cheat women out of thousands of dollars, the US Army's Criminal Investigation Command has warned.

Special CID agents cautioned that they had learned of multiple incidents in which people online posed as US soldiers and got "romantically involved... with female victims and prey on their emotions and patriotism."

Army CID spokesman Chris Grey said the scammers often used information about real soldiers, including their names and ranks, and found photographs of soldiers online to create a false identity.

These individuals promise "true love, but only end up breaking hearts and bank accounts," the CID warned.

Once they have snared a victim, the criminals request money they claim is needed to purchase items including laptops and return plane tickets.

"These perpetrators, often from other countries, most notably from Ghana, Angola and Nigeria, are good at what they do and quite familiar with American culture," said Grey.

The Army CID warned women to be cautious when contacted online by people claiming to be US servicemembers.

"Be extremely suspicious if you are asked for money for transportation costs, communication fees or marriage processing and medical fees," the CID warned in a statement.