Police are issuing an air and sea port warning amid fears five monkeys that were stolen from Blackpool Zoo will be smuggled out of Britain and sold.
Police believe the rare animals were stolen in a "planned and pre-mediated break in".
Two female and one baby cotton-top tamarin, which are a critically endangered species, and two male emperor tamarins were stolen overnight on Tuesday.
Police say all ports and airports have been placed on alert in case the thieves try to take the animals abroad.
"It would appear from the way that these thieves have broken into the zoo that this was a planned and pre-meditated crime and that the offenders knew what they were looking for and knew that the monkeys would be in the enclosures," said Pc Steve Higgs, of Blackpool Police.
Police added the stolen monkeys "need specialist care" and said officers are working with the National Wildlife Crime Unit to try to trace them.
Blackpool Zoo said they are "extremely saddened by the theft of these monkey" and say it is that the rare monkeys receive the "correct care in order to survive".
Andy McWilliam, investigations officer at the National Wildlife Crime Unit, said: "There is definitely a market for these monkeys and we are making inquiries across Europe in a bid to try and trace them."