U.S. Senate Judiciary Committee Chairman Patrick Leahy said on Thursday he would issue a subpoena for President George W. Bush's top political adviser Karl Rove to testify before Congress over the firings of nine federal prosecutors last year.

"We have now reached a point where the accumulated evidence shows that political considerations factored into the unprecedented firing of at least nine United States Attorneys last year," Leahy said.

Leahy was also issuing a subpoena for J. Scott Jennings, a White House political aide.

Leahy, a Democrat from Vermont, said that for over four months, he had exhausted "every avenue seeking the voluntary cooperation of Karl Rove and J. Scott Jennings, but to no avail."

He accused the White House of stonewalling requests for information regarding the dismissals, which many lawmakers said might be politically-motivated instead of what the administration had insisted as to performance-related.

"Indeed, the White House is choosing to withhold documents and is instructing witnesses who are former officials to refuse to answer questions and provide relevant information and documents," Leahy said.

At the White House, spokesman Tony Fratto said congressional Democrats were "more interested in headlines than doing the business Americans want them to do."

Nine federal prosecutors were fired last year, most of them after the mid-term congressional elections in November.

While administration officials said the attorneys were ousted over concern about their performance, lawmakers suspected that they were targeted because they had not carried out the political agenda of the Republican Party, particularly before the mid-term elections last November.

Both the Senate and the House were investigating the firings, but the Bush administration invoked executive privilege this month to refuse requests by Congress that Bush's former counsel Harriet Miers and former political adviser Sara Taylor testify in the probes.