Kabul - A frustrated Afghan soldier who could not afford to get married has been released without charge after being caught having sex with a donkey, police said on Tuesday.

The soldier, who was not identified, was detained for several days last week after a young boy spotted him with the animal in an abandoned house in the south-eastern town of Gardez.

"The man insisted he had no other choice but the donkey because he could not afford to pay a dowry to get married," a local police officer said.

The man had since been released without charge, he said.

In many parts of Afghanistan men must pay at least $3 000 (about R20 000) to the parents of their prospective bride, making marriage difficult for many in a country where the average annual income is only a few thousand rand.

Under the strict Islamic rule of the fundamentalist Taliban regime overthrown in 2001, sex outside of marriage or bestiality were punished by stoning to death or flogging.