A pigeon is in Bosnian police custody after learning prisoners were using the bird to smuggle drugs into one of the country's highest security jails, AFP reported.

"The guards suspected the animal might be involved in drug smuggling once they noticed four prisoners visibly intoxicated shortly after the pigeon landed on a prison window," Zenica prison official Josip Pojavnik told AFP.

Pojavnik said the drugs were likely stuffed into tiny bags that were then attached to the legs of the carrier pigeon, according to the report.

One of the inmates had previously been allowed to a carrier pigeon as a pet in his cell, he added.

Four prisoners tested positive for heroin and disciplinary proceeding had been launched against them, AFP reported.

"We do not know what to do with the pigeon, but for the time being it will remain behind bars," Pojavnik said.

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