Violence is down 55% in Iraq since the US troop build-up began this summer, but it is unclear what role Iran played in the downturn, US officials said today, tempering recent optimism about Tehran’s waning support for militants with warnings that more needs to be done.

US SECRETARY of State Colin Powell and his top deputy have told the White House they will not serve a second term if President George W Bush is re-elected, The Washington Post reported.