Police warned yesterday that time was running out for five rare monkeys stolen from a zoo over the weekend.

Thieves broke into Drusillas, near Alfriston, between 6pm on Saturday and 8am on Sunday and took the marmosets as they slept.

Manager Sue Woodgate said keepers are especially concerned for Jazz, the mother monkey, who will die without a twice daily medication for an infection.

Sue also fears for Jazz's baby Larkin, who is dependent on his mother. She said: "We are very worried about the welfare of all the monkeys.

"I was so angry when I first found out, then the tears started. I don't really hold much hope at all. They're professionals. They knew exactly what they were doing."

Marmosets, which originate from the Amazon basin and across South America, are on the worldwide list of endangered animals. They are worth anything from a few hundred pounds to £3,000 on the black market.

Organised gangs have been known to target smaller zoos with less security. John Hayward, co-ordinator for the National Theft Register for Exotic Animals, is working with the zoo.

He suspects the break-in was a professional theft carried out "to order". More than 50 small monkeys have been stolen over the past three years.

He said: "They are not pets, but they could end up being traded for breeding purposes. They could easily end up in some aviary or shed."

Mr Hayward believes the theft may be linked to a similar incident at Exmoor Zoo, Devon, in March.

Up to 13 similar monkeys were seized by burglars in the raid, including two thumb-sized youngsters. They were never found.

Curator of Exmoor Zoo Daniel Reynolds said: "They just disappeared into thin air. We're near a ferry port, so I suspect they were taken out of the country."

Mr Reynolds said he did not foster much hope for the survival of Drusillas' marmosets.

He added: "If they were stolen to order and taken to a home, then that's better.

"But if they were taken to be hiked across the Continent to be sold, they'll be dead within a day."

Sussex Police issued a warning not to approach the monkeys if spotted. They are not considered dangerous but are not domesticated. Anyone with information should call 0845 6070 999.