Arrests have been made as part of a counter terrorism probe after suspicious packages were sent to NHS hospitals.
Leeds Teaching Hospitals has confirmed that it received one of the packages and the incident is being investigated by the Metropolitan Police.
Two men have been arrested in London after hospitals around the country received packages containing a liquid substance, police said.
A Leeds Teaching Hospitals spokeswoman said: "We followed our usual protocols and it is now being dealt with the police and NHS England."
The Metropolitan Police said two men were arrested on suspicion of Malicious Communications Act offences.
A spokesman said: "None of the packages have so far been found to contain anything hazardous.
"Officers from the Met's Counter Terrorism Command arrested a 29-year-old man from Brent and a 37-year-old man from Harrow at approximately 6.45pm yesterday, (August 2).
"They were both arrested in Barnet and taken into custody at a north London police station. They were subsequently bailed to return to a north London police station in late August.
"Enquiries are ongoing."