Arizona and California were helped by the US Food and Drug Administration to get supplies of a hard-to-find execution drug from the UK.
A shortage of sodium thiopental has disrupted executions around the US.
New documents show the Food and Drug Administration (FDA) helped Arizona import the drug from an English company in the autumn.
Californian prison officials said the federal agency released a batch of the drug last week that the state also bought from the UK.
The FDA will not comment on its role in helping either state. The agency says it does not regulate products used in lethal injection.
Alabama, Oklahoma and Texas plan executions this week. Alabama and Texas use sodium thiopental, but Oklahoma uses a different drug.