The United Nations Security Council agreed last weekend to sanction Iran for refusing to suspend its uranium enrichment program. The unanimous vote is designed to encourage Tehran to cooperate with the International Atomic Energy Agency (IAEA) and eliminate suspicions about its nuclear intentions. The vote is a proper step forward -- an escalation of pressure -- but Iran's continuing defiance means the world had better be ready for, and prepared to respond to, more provocations from Tehran.

There have been doubts about Iran's nuclear program since its inception, but concerns have intensified following a steady drip of revelations about secret facilities and capabilities. Years of negotiations to find a formula that would permit Iran to build a peaceful nuclear program while ensuring that it could not be diverted for military purposes have made no progress. Three months ago, frustrations bubbled over and the U.N. Security Council adopted a resolution that banned trade in sensitive nuclear materials and ballistic missiles, and froze the assets of 12 individuals and 10 institutions associated with the nuclear programs.

That resolution called for a halt to Iranian efforts to enrich uranium and the reprocessing of spent nuclear fuel, both of which can be used to build nuclear weapons. Tehran refused to suspend the programs, arguing that as a signatory to the Nuclear Nonproliferation Treaty (NPT) it has a right to technology for the peaceful use of nuclear energy. That is not in dispute. The question is whether Iranian intentions are truly peaceful; on that count, all the world has is Iranian assurances, which are not worth much in light of the revelations about hidden programs.