U.S. Defense Secretary Donald Rumsfeld paid a surprise visit to Iraq on Friday and told U.S. troops the war could still be won. He saw victims of a suicide bombing at a U.S. base in Mosul and troops who stormed the city of Falluja last month, after flying in in great secrecy on a trip that took in four cities and wound up in Baghdad. Under fire at home, he assured the troops of his "respect" for them and told them he was doing all he could to improve their equipment -- a sensitive topic many asked about. His trip began in Mosul, where he pinned a Purple Heart medal on one of dozens wounded when a suicide bomber in Iraqi uniform blasted a mess tent on Tuesday, killing 22 people, 18 of them Americans. It was the costliest single incident for Americans since the start of the war. The attack, which has hit Americans' trust in the very Iraqi forces they hope to train to take over from them, highlighted the continued potency of an insurgency that the assault on Falluja was supposed to quell before next month's election. --More 2132 Local Time 1832 GMT