The National Gallery in London announced on Thursday that it is strengthening security measures after becoming the target of protests by environmental and pro-Palestinian activists who have attacked works from its collection.

The institution stated that it had been “the victim of five different attacks” since July 2022. The artworks, which are protected by glass, were not damaged in these incidents, although in some cases their frames were destroyed.

“Unfortunately, we have reached a point where we are obliged to take measures to protect our visitors, staff, and collection,” the museum explained in a press release.

Starting tomorrow, “no liquids will be allowed in the National Gallery,” except for baby formula and prescription medications, it noted.

Entry to the National Gallery, located in the heart of London near Trafalgar Square, is free, as with all public museums in Britain. Visitors pass through a security gate, and a police officer may inspect their bags.

This announcement comes a week after two pro-Palestinian activists from the group Youth Demand briefly covered Picasso’s painting Maternity (1901) with a photograph showing a mother and her child, both bloodied, in the Gaza Strip.

At the end of September, two environmental activists from the “eco-terrorist” group Just Stop Oil threw soup at two of Van Gogh’s Sunflowers paintings. Two members of the same group had done the same to one of the Sunflowers replicas in July 2022, and were sentenced to prison.

In its announcement, the National Gallery also referred to incidents against John Constable’s The Hay Wain in 2022 and Diego Velázquez’s The Rokeby Venus in 2023.