Talks between the United Nations nuclear watchdog and Iran on an agreement to monitor the latter’s nuclear program have ended without progress.

Negotiators for the UN International Atomic Energy Agency left Iran Tuesday after two days of talks, and without being allowed to inspect the Parchin military base near Tehran, a military site thought to be used for explosives testing.

The failure comes in the wake of increasingly tough sanctions against Iran by the international community.

Iran’s Supreme Leader Ayatollah Ali Khamenei vowed to move ahead with the country’s nuclear program.

“With God’s help, and without paying attention to propaganda, Iran’s nuclear course should continue firmly and seriously. Pressures, sanctions and assassinations will bear no fruit. No obstacles can stop Iran’s nuclear work,” he said on state television.

Iran last week sent a letter to European Foreign Policy chief Catherine Ashton saying it would bring new initiatives to the talks.