Iran apparently has assured the Iraqi government that it will stop the flow into Iraq of bomb-making materials and other weaponry that US officials say has inflamed insurgent violence and caused many American troop casualties, Defense Secretary Robert Gates said Thursday. "It is my understanding that they have provided such assurances," Gates told a Pentagon news conference. "I don't know whether to believe them. I'll wait and see." He said he did not know who in Tehran made the promise. Gates also offered one of his most upbeat assessments of the overall state of US efforts to stabilize Iraq, saying security is improving significantly even as Iraqi political progress at the national level lags. "Clearly the direction in Iraq is headed in a significantly more positive direction than it was five or six months ago," he said.