Thieves carried out a well-organized, pre-dawn heist at Greece's biggest state art museum on Monday, taking two oil paintings by Pablo Picasso and Piet Mondrian.

An AP report says that the burglars entered through a balcony door and also took a pen and ink drawing of a religious scene by Italian 16th century painter Guglielmo Caccia. It said a fourth work by Mondrian also was removed from the National Art Gallery in one of the best-guarded areas of central Athens, but the thieves abandoned it as they fled.

Museum officials were unable to immediately estimate how much the stolen works were worth.

The burglars still triggered a sensor in the exhibition area, but a guard only got there in time to see a man running off, said the report.

The art gallery had been due to close Monday for a long period of extension and refurbishment.