Bulgarian authorities have shut down a workshop with devices for stealing credit card information and making fake documents, and arrested four suspects, the country's interior ministry said in a statement on Monday.

The workshop with a "fully closed production cycle" was revealed on Friday in a settlement near Plovdiv, some 150 km southeast of Sofia, the statement said.

Law enforcement officers found evidence such as computers with programs for processing and storing information illegally taken from bank cards, micro-cameras, ATM slots and keyboards, and POS terminals, the statement said.

"A large amount" of Bulgarian and foreign documents like passports and identity cards, as well as blank identity documents, were also discovered, it said.

Searches of eight houses in the region near Plovdiv were carried out, it said.

The data collected so far indicated that the suspects have been active in their illegal work since January 2017, the statement said.

The investigation continues.