British police are investigating a suspected attempt to sabotage Britain’s railway lines that’s believed to be linked to pro-Brexit sentiment. Two homemade short-circuit devices were found clipped to railway tracks in Cambridgeshire and Nottinghamshire, England, last week. The devices, which police deemed “malicious obstructions,” were discovered with a note saying “leave means leave.” It threatened to “bring this country to its knees” if Britain doesn’t exit the European Union, according to The Mirror newspaper. The devices were designed to tell workers that a train was stationary on the track even if there wasn’t one, disrupting the network and causing delays. Safeguards introduced to comply with EU regulations caused the devices to fail. British Transport Police said they were working “tirelessly” to catch those responsible, but no arrests have been made. “This was a serious and deliberate attempt by someone to cause significant sabotage and disruption to Britain’s rail network,” said Sean O’Callaghan, assistant chief constable of the British Transport Police.