Iran was signing a deal today to open up its nuclear activities to international scrutiny, agreeing to intrusive inspections in a bid to challenge US claims that it is secretly developing nuclear weapons.

With the signing of an unprecedented agreement by an Iranian representative and International Atomic Energy Agency chief Mohamed El Baradei, Tehran sought to lay to rest lingering suspicions about its nuclear programme.

The United States has called Iran part of the global ”axis of evil”, accusing Tehran of trying to develop nuclear weapons. Iran insists that its atomic energy program is peaceful and geared purely towards generating electricity.

Yesterday, Iranian vice president Gholamreza Aghazadeh said Tehran had nothing to hide.

“We have agreed to sign … to give a strong response to accusations against us and demonstrate that our nuclear activities are peaceful,” he said in Tehran.

Since October, Iran repeatedly has said it would sign the accord, but its failure to follow through had led to speculation that it might be stalling.

The agreement, tacked on to the Nuclear Non-proliferation Treaty, requires Iran to submit to intrusive and unannounced United Nations inspections of its nuclear complexes and research facilities.

Iran agreed last month to open suspect sites that up to now have been off-limits, and to let IAEA inspectors conduct surprise checks to ensure the country is not trying to develop atomic weaponry as the United States claims.

The IAEA’s 35-nation board of governors censured Iran in November for 18 years of secrecy in a resolution that warned Tehran to stay in line with international efforts to make sure the country has no nuclear weapons ambitions.

The resolution did not confront Iran with a direct threat of UN sanctions – a tougher approach that Washington had sought. However, it did warn Tehran that the IAEA would consider further action if “further serious Iranian failures” arose.

The wording implicitly warned Iran that the agency could report it to the UN Security Council, which has the power to impose economic or diplomatic sanctions.

US State Department spokesman Richard Boucher said Washington welcomed Iran’s signing of the pact, but warned that it was “only one step towards resolving the remaining open questions about Iran’s nuclear programme”.