Iran's top nuclear negotiator has ruled out halting Tehran's uranium enrichment work, saying that "suspension is not a way" to resolve Iran's nuclear standoff with the West.

Ali Larijani spoke to reporters at Tehran airport Wednesday, before departing for Spain for another round of nuclear talks with European Union foreign policy chief Javier Solana. They are to meet in Madrid on Thursday.

The two men have held several rounds of talks on the issue but there have been no reports of progress.

Iran has continued to defy international demands to halt enriching uranium - a process that can produce material suitable for building nuclear weapons.

The United States is leading international efforts to impose tougher sanctions against Iran for ignoring the latest U.N. Security Council deadline of May 24 to stop the sensitive nuclear work.

Iran is already under limited U.N. sanctions for failing to meet earlier Security Council resolutions.

The United States and its allies accuse Iran of trying to develop nuclear weapons - a charge Iran denies.