The outspoken Republican Senator John McCain has said he has "no confidence" in Defence Secretary Donald Rumsfeld over his handling of the war in Iraq.
McCain has made disparaging remarks about Rumsfeld before
Mr McCain said there were "strong differences of opinion" between the two men, particularly over troop numbers.
But he refused to call for Mr Rumsfeld to resign, saying who was in the team was up to President George Bush.
Mr Rumsfeld faced a public grilling from his own troops when he visited a US base in Kuwait last week.
The BBC's correspondent at the Pentagon, Nick Childs, says those complaints have continued to reverberate in Washington and the latest attack has put Mr Rumsfeld back in the focus of controversy.
In an interview with the Associated Press news agency, Mr McCain was asked whether he was confident in the secretary's leadership.
He said he remembered responding to a similar question recently: "I said no. My answer is still no. No confidence," he said, according to the agency.
Mr McCain said he believed a further 80,000 army personnel and 20,000 to 30,000 more marines were needed to secure Iraq.
"I have strenuously argued for larger troop numbers in
Iraq, including the right kind of troops - linguists,
special forces, civil affairs, etc.," Mr McCain said.
"There are very strong differences of opinion between
myself and Secretary Rumsfeld on that issue."
But Mr McCain refused to say whether Mr Rumsfeld constituted a liability to the Bush administration.
Last week, Mr Rumsfeld was publicly grilled by troops who alleged they used scrap metal to armour vehicles.
The row prompted new calls for his resignation from long-time opponents, including senior Democratic congresswoman Nancy Pelosi.
This is not the first time Mr McCain has spoken plainly of his disquiet about Pentagon policy under Mr Rumsfeld, but his remarks underline that there is unease in Republican ranks too, says our Pentagon correspondent.
Rumsfeld recently faced a grilling from US soldiers
Even so, Mr Rumsfeld's job is probably safe for now, says our correspondent, since he has only just accepted a request from a newly re-elected Mr Bush to stay.
However, these latest political rumblings reflect renewed worries in Washington about the effectiveness of the overall US policy in Iraq, our correspondent adds.