The White House and Democrats dug in their heels on Wednesday in the battle over whether top aides to President George W. Bush – including Karl Rove – will co-operate with a congressional investigation into the controversial sackings of eight top prosecutors late last year.

A House of Representatives subcommittee on Wednesday authorised subpoenas that would require Mr Rove and Harriet Miers, the former White House counsel, to testify under oath about the affair.