Police in the southern Indian city of Hyderabad are investigating the theft of a gold, diamond-studded lunchbox that belonged to a former royal family.

The thieves also stole a ruby and gold teacup, saucer and teaspoon. Weighing 3kg, the items are valued at about $7m.

They belonged to Mir Osman Ali Khan - the last Nizam (king )of Hyderabad - and once the richest man in the world.

The theft was discovered on Monday morning. Police suspect it occurred the previous night.

The valuables were removed from their display vaults in the Nizam's palace, which is now a museum.

A sword belonging to the same royal family was stolen from another museum in the city 10 years ago.

Police told BBC Telugu that they suspect two people were involved in the latest theft.

According to the Hindustan Times, police told local reporters the thieves tampered with CCTV cameras so there would be no recording of the raid. They added that the glass door to the cabinet that contained the items was unscrewed to avoid damage.

The items were in the Nizam Museum, which opened to the public in 2000. Its collection comprises expensive gifts given to Mir Osman Ali Khan in 1937.

Khan ruled what was then India's largest princely state. He died in 1967.

His fabled wealth included the world-famous Jacob's Diamond - which was the size of an egg - in addition to many other pieces of exquisite jewellery.