The US is threatening to tighten sanctions on Iran over a newly disclosed uranium enrichment site near the Iranian holy cit of Qom. On Friday, Iran acknowledged the site’s existence but said no nuclear enrichment had taken place. The Iranian government says it hasn’t violated its international commitments because it’s only required to disclose a nuclear site six months before it becomes operational. The Obama administration has warned of “severe” sanctions unless Iran suspends work on the site and allows international inspectors. In his weekly radio address, President Obama said he remains open to dialogue with Iran but warned of punitive action.

President Obama: “This is a serious challenge to the global nonproliferation regime and continues a disturbing pattern of Iranian evasion… My offer of a serious, meaningful dialogue to resolve this issue remains open. But Iran must now cooperate fully with the International Atomic Energy Agency and take action to demonstrate its peaceful intentions.”

The spat over Iran’s nuclear program comes just days before Iranian officials will meet counterparts from the US and five other countries. Earlier today, Iran also said it had successfully tested long-range missiles following a short-range missile test on Sunday.