A woman and her husband have been detained in southern Russia after they kept the woman's father, 70, on a chain in their yard for four days, investigators said Wednesday.

The couple "tied him to a tree with a metal chain in their yard and kept him there from July 28 to August 1," the Investigative Committee said in a statement.

It published photographs of a thin grey-haired man sitting on a mattress with a chain attached to his foot and of the couple's one-story detached house in a rubbish-strewn yard in the southern Rostov region.

"Neighbours heard his cries for help and called law enforcers," investigators said.

Investigators confiscated as evidence the 3.5 metre chain, as well as his aluminium drinking cup and a plastic water bottle and launched a probe into illegal imprisonment.

"This outrageous case causes deep horror," investigators said.

The man's daughter, 41, "had grown tired of taking care of the blind and deaf man and simply took him out into the yard and chained him up," the Life News website reported, adding that the couple's children were witnesses.

Outside temperatures reached 50 degrees centigrade (122 degrees Fahrenheit), Life News reported.