The Arizona attorney general’s office says the state’s supply of a scarce lethal injection drug was obtained from England.

This is the first time a state has acknowledged obtaining sodium thiopental from an overseas source since a shortage of the drug started affecting executions in the U.S. this year.

Chief Deputy Attorney General Tim Nelson told The Associated Press on Tuesday that the state revealed the drug’s origins to let the public know it comes from a trustworthy source.

Jeffrey Landrigan’s execution was scheduled for Tuesday morning. But it remains on hold after a federal judge delayed the lethal injection because of questions about the drug’s origins.

Landrigan’s lawyers are challenging the use of the English drug because it is not approved by the U.S. Food and Drug Administration.