Iran's national carrier, Iran Air, said on Tuesday it had been forced to ground almost one-third of its fleet of Airbus planes because US sanctions had prevented it from securing spare parts.

Washington agreed in March to ease its tough sanctions and allow some civilian aircraft parts sales to the Islamic state in support of a European Union package of incentives aimed at persuading Tehran to abandon its atomic program.

But the EU talks with Iran have since broken down and there have been no reports of any aircraft parts being sold to Iran under this case-by-case waiver.

"We have grounded five Airbuses out of 16 because we are unable to purchase the engines," said Malek Barzegar-Sedigh, Iran Air spokesman. Iran Air's Airbus engines are US-made.

He accused Washington of putting passenger safety at risk.

"The country which boasts more than any other country about human rights endangers many invaluable lives by resorting to such political measures."

Unable to buy new aircraft or spares from the West, Iran has supplemented its fleet of Boeing Airbus planes with aircraft from former Soviet Union countries.

Iran has a poor airline safety record, according to air safety experts. Some foreign companies operating in Iran discourage their employees from taking certain types of aircraft on internal routes or using Iran Air for international flights.

Barzegar-Sedigh said Iran Air had formed a Counter-Sanctions Committee charged with finding ways to get around the sanctions and obtain spare parts.

US sanctions on Iran do allow for the sale of spare parts related to the safety of civilian aircraft -- but only if the aircraft themselves are of US origin. At the same time they bar the export of any US parts to Iran which would constitute more than 10 percent of the value of the finished product.