Zookeepers in the Czech Republic are struggling to get two frightened female frogs to come out of their cages after bringing in a giant three-pound bullfrog to mate with them.

The rare burrowing bullfrog, found in southern Africa, was introduced to two females of the same species at Plzen zoo last week.

But the two females immediately ran for cover and buried themselves in the ground at the bottom of their cages when they saw the size of the bullfrog, Czech agency CTK reported.

Zoo spokesman Martin Vobruba said: "We placed the male and his two wives in a section of the zoo called The Mysterious World of the African Night. The females, however, have shown no enthusiasm so far."

Chief zoologist Vitezslav Honsa added: "We even went as far as getting a tape for them with frog sounds on it so they could make love."