ATHENS, Greece — A Greek couple has been arrested for buying a Roma baby girl from her mother for 4,000 euros ($5,500) and they will appear before a prosecutor on Friday to face charges, police said.

It is the third case of suspected baby trafficking uncovered in Greece since last week, when authorities discovered a blond four-year-old girl in a Roma camp who did not resemble the family she was living with.

The discovery of Maria, dubbed the "blonde angel" by Greek media, sparked a global search for her real parents after DNA tests showed the Roma couple she was with were not her blood relatives.

The Greek couple, who were arrested in Athens on Wednesday, are not Roma and claimed they bought the child in March because they had no children, the police said in a statement.

"The baby has been with them since then while they sought ways to legalize it," the police said. The two suspects are aged 53 and 48.

Trafficked babies are usually bought in Greece from mothers from impoverished former communist countries, especially neighboring Bulgaria. They are usually legalized through false statements at birth registries or courts.

Greece earlier this week ordered a nationwide birth certificate investigation to track down such cases.

Greece and Bulgaria agreed on Thursday to step up efforts against baby trafficking between the two countries.

Bulgarian authorities also said on Thursday they were investigating a Bulgarian Roma woman they suspect of being the natural mother of Maria and of having sold the child.