A £500,000 bronze sculpture by the leading British artist Henry Moore has been stolen from the grounds of his former home.
Sundial 1965 was taken some time late on Tuesday or early on Wednesday from the garden at the Henry Moore Foundation in Perry Green, said Hertfordshire Police.
The force said that as yet it is not known whether the 22in (56cm) sundial, which is made up of two interlocking bronze crescents, was stolen by someone wanting to sell it as a work of art or for its scrap value.
Richard Calvocoressi, director of the foundation, said: "We are deeply saddened about the loss of Sundial from the gardens of Henry Moore's former home and are helping the police in the hope it may be recovered.
"We take care of our Henry Moore's sculptures extremely seriously and have installed heightened security measures here in recent years. We would be grateful if anyone with information would contact the police."
It is the latest work by the abstract artist, who died in 1986 aged 88, to be targeted by thieves.
The Foundation carried out a security review following the theft of a Moore bronze in December 2005 from its own estate.
The two ton Reclining Figure 1969-70 - insured for £3 million - was lifted by crane on to a lorry and has not been recovered.
In 2010, Moore's £45,000 painting, Three Reclining Figures On Pedestals, was one of three works of art worth a combined £230,000 stolen from a gallery in Broadway, Worcestershire.
Sundial 1965, which was a working model for much larger sculptures, is believed to have been stolen between 4.30pm on Tuesday July 10 and 11am the following day. It is valued at between £250,000 and £500,000, police said, although its scrap value would be far less.