The high Sunni turnout for Iraq's constitutional referendum, coupled with the low level of violence, demonstrated that the United States was making strong progress in Iraq, the US ambassador to Iraq said. "I think the important achievement of yesterday, which was a great day for Iraq, was that the Sunnis, who had not participated in the political process, did participate this time," Zalmay Khalilzad said on ABC television on Sunday. "I think we are making good progress. Yesterday was a good indication that our approach to the Sunnis is producing results." "This is the first time, yesterday, that they have participated in significant numbers," said Khalilzad, who had a key behind-the-scenes role in bringing about the draft and the referendum. More than 61% of registered Iraqi voters took part in Saturday's referendum on a permanent constitution, which, if approved, will open the way for general elections in December for a new government.