US Vice-President Dick Cheney has insisted that the recent increase of US troops in Iraq, or "surge", has improved security there.
Mr Cheney said the insurgency had been stronger than he expected
In an interview with CNN, Mr Cheney said he believed a report on the US-led crackdown, due in September, would reveal significant progress.
Official figures showed 74 American service members died in Iraq in July, the lowest figure since late last year.
US troop numbers have been boosted by 30,000 since the start of the year.
Mr Cheney said he expected the report compiled by the US military commander in Iraq, David Petraeus, and Ambassador Ryan Crocker to be positive.
"The reports I'm hearing from people whose views I respect indicate that the Petraeus plan is in fact producing results," Mr Cheney told CNN.
President George W Bush has refused to speculate about the September report, saying on Monday: "I don't want to pre-judge what David is going to say."
The vice-president admitted that he had been wrong when he said in May 2005 that the armed insurgency in Iraq was "in its death throes".
"I think my estimate at the time was wrong," Mr Cheney said. "That clearly didn't happen. I think the insurgency turned out to be more robust."
The White House and Congress have clashed over Iraq withdrawal
The Petraeus-Crocker report is due to be presented before Congress on 15 September.
Democrats, who are in control of both the House of Representatives and the Senate, want President George W Bush to come up with a military withdrawal plan from Iraq for 2008.
But the man Mr Bush has nominated as chairman of the joint chiefs of staff, Michael Mullen, has predicted that the US will be in Iraq for years, not months, and he warned Congress against attempts to secure a rapid pull-out of troops.