The National Gallery has banned liquids - except baby formula, expressed milk and prescription medicines - after attacks by activists on its artworks, including Vincent van Gogh's Sunflowers.
The new measure comes into force today.
The London museum also urged visitors to bring "minimal items" to the premises, and "no large bags".
"Unfortunately, we have now reached a point where we have been forced to act to protect our visitors, staff and collection," it said in a statement.
The museum cited several attacks on artwork since July 2022, including on John Constable's The Hay Wain and Velazquez's Rokeby Venus, as well as on the Sunflowers.
"Such attacks have caused physical damage to the artworks, distress to visitors and staff alike, and disruption to our mission to ensure great art is available for everyone, everywhere to enjoy," it said.
"Two of these attacks have happened in the last two weeks, and that is why we have taken the difficult and unfortunate decision to change the way we operate for the foreseeable future."
The museum also said: "All doors into the gallery have walk-through metal detectors where we will inspect bags and rucksacks," adding that entry would likely take longer as a result.
Last month two versions of the Dutch master's famous Sunflowers were hit by soup.
Neither painting was damaged but prosecutors said the frames were, for an estimated worth of £10,000 to £20,000.
Three Just Stop Oil supporters have pleaded not guilty to criminal damage.
That incident happened after two Just Stop Oil activists were jailed for causing up to £10,000 worth of damage to the frame of one of Van Gogh's Sunflowers at the gallery in October 2022.
Separately, two activists glued themselves to Constable's The Hay Wain in July 2022.
In November last year, protesters allegedly smashed the glass protecting the Rokeby Venus, or The Toilet of Venus, and caused more than £6,000 of damage.
(c) Sky News 2024: National Gallery in London bans liquids after activists' attacks on Sunflowers and other artw
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