Karl Rove, the former political adviser to President George W. Bush, was subpoenaed on Thursday by a congressional committee investigating if the White House ordered prosecutors to target a former Democratic governor for political reasons.

John Conyers, the chairman of the House judiciary committee, ordered the move after Mr Rove’s attorney said his client would not voluntarily appear to answer questions about the prosecution of Don Siegelman, the former Alabama governor who was convicted in 2006 of bribery and obstruction.