Iran signed a legal agreement Thursday giving the International Atomic Energy Agency broader access to nuclear facilities and related sites, suspected by the United States to be a cover for a nuclear weapons program.

Iranian envoy Ali Akbar Salehi signed the so-called additional protocol to the Nuclear Non-Proliferation Treaty at a ceremony attended by IAEA director Mohamed ElBaradei.

Mr. Salehi said this was an historic moment for his country and a turning point for the IAEA.

"I ardently hope that a new stage is set and that my country shall no more be subject to unfair and politically motivated accusations and allegations," he said. "We have committed ourselves to fully fledged co-operation with the agency."

Mr. Salehi went on to say that the entire Iranian government supported full transparency with the U.N. nuclear agency and would leave no stone unturned in disclosing details of its nuclear program.

The United States believes Iran has worked on a secret nuclear weapons program for almost two decades. The IAEA board said last month that Iran has engaged in a pattern of deception about its nuclear program for the past 18 years.

Mr. ElBaradei told reporters there is much work to do in Iran in the upcoming months.

"The protocol is clearly a very important tool to enable us to provide assurances expected by the international community," said Mr. ElBaradei. "I think it's an important building block towards establishing confidence that Iran's program is exclusively for peaceful purpose."

Mr. ElBaradei said Iran has provided full access to nuclear facilities since mid-October and is already acting as if the protocol were in force.

The protocol has yet to be ratified by the parliament in Tehran.

At its meeting last month the IAEA board welcomed Iran's new co-operation with the agency, but warned that any further failure to cooperate could trigger U.N. Security Council involvement and possible sanctions.