The U.S. government on Sunday turned down a proposal from two top Republican lawmakers to start withdrawing U.S. troops from Iraq by this year-end, saying it is too early to change its Iraq strategy.

Appearing on "Fox News Sunday," President George W. Bush's national security adviser, Stephen Hadley, ruled out any consideration to change Iraq policy before September, when the second progress report on Iraq is scheduled to come out.

He was responding to a proposal unveiled by Republican Sens. John Warner of Virginia and Richard Lugar of Indiana on last Friday that recommends a possible troop draw down or redeployment by the end of the year.

Asked about whether Bush could live with the proposal, Hadley responded with "No."

The Bush administration is under growing pressure on the troop withdrawal issue in the wake of an interim progress report released last week which concluded that the Iraqi government has failed to meet key political, economic and security goals set by the United States.

Warner and Lugar's move represents a growing uneasiness within the Republican camp towards Bush's insistence to keep his cause.