The international demand that Iran halt uranium enrichment before negotiations on its nuclear program can begin is unnecessarily blocking diplomatic progress, a series of speakers said at a conference on weapons proliferation Monday. While disagreeing on other issues, former chief UN weapons inspector Hans Blix; Council on Foreign Relations President Richard Haass, a former senior State Department official in President George W. Bush's administration; and Iran's UN ambassador all criticized the demand that Tehran stop enriching uranium before negotiations can go forward. Blix said the United States, Europe and the UN Security Council were "humiliating" Iran with the precondition. "This is in a way like telling a child, first you will behave and thereafter you will be given your rewards," Blix said. "And this, I think, is humiliating."