Violence is down 55 percent in Iraq since the US troop buildup early this summer, but it is unclear what role Iran played in the downturn, US officials said Sunday. Washington has accused Iran of training, arming and funding Shi'ite extremists inside Iraq. In recent weeks, US officials have said Teheran appears to have halted the flow of arms across its border into Iraq. But US officials said Sunday that it was too early to determine Iran's role in a recent sharp downturn in violence. "It's unclear to us what role the Iranians might have had in these developments, if any," said Philip T. Reeker, spokesman for the US Embassy in Baghdad.