Monkeys stolen from a zoo could have been targeted by a criminal gang to meet demands of private collectors intent on building up a Noah's Ark of exotic animals.

The theft of five rare primates from Drusillas, in Alfriston, near Polegate, overnight on June 17 and 18 has reignited concerns at the scale of the problem.

Forty per cent of zoos across Europe have reported being hit by animal thieves and the Marmosets from Drusillas has brought the number of stolen monkeys to 80.

Staff at the zoo are especially concerned for Jazz, a rare Silvery Marmoset, who has recently given birth and was being given antibiotics for an inflamed jaw.

She was due to have an exploratory operation once Larkin, her two-month-old baby, was weaned.

Claire Peters, PR and marketing officer at Drusillas, said: "Looking after a primate is a specialist area and people may not realise what is involved.

"We are very concerned about Jazz and her baby because without the right care they could both die.

"The mood here is sombre as a lot of the staff had formed emotional attachments with the monkeys. It is absolutely awful and everyone is devastated.

"On their enclosure we have put up a notice to let visitors know why it is empty. Their support has been fantastic. We are hoping someone will come forward with information."

Marmosets originate from the Amazon basin in South America and are on the worldwide list of endangered animals.

They are worth up to £3,000 on the black market.

John Hayward, coordinator of the National Theft Register for Exotic Animals, believes zoos are facing highly professional gangs that steal animals to order.

The police investigation into their disappearance is continuing and officers are following several lines of inquiry.

A spokeswoman said: "Concern for their welfare is growing especially as one of the monkeys requires medication twice daily to survive. It is imperative these monkeys are found as soon as possible.

"Police would like to remind people that although the monkeys are not considered dangerous and have been bred in captivity, they are not domesticated in any way.

"If anyone sees the monkeys please do not approach them. Instead contact the police immediately."

Anyone with any information is asked to contact police on 0845 6070999 or Crimestoppers on 0800 555111