The United States is investigating whether Iran sent hundreds of special artillery shells for chemical weapons to the late Moamer Kadhafi regime in Libya, The Washington Post reported late Sunday. The shells, which Libya had filled with mustard gas, were discovered in recent weeks at two sights in central Libya, the Post said citing unnamed US and Libyan officials. US intelligence is leading a probe of the origin of the shells, the report added. \"We are pretty sure we know\" that the shells were designed and produced in Iran and intended Libya, a senior US official told the newspaper said on the condition of anonymity. Another US official told the Post there were \"serious concerns\" that Iran had provided shells, but it had occurred some some years ago, said the report. Potential evidence that Iran supplied the specialized shells could fuel further worries about Tehran\'s alleged pursuit of weapons of mass destruction. A November 8 IAEA report strongly suggested Iran -- despite its repeated denials -- was researching nuclear weapons under cover of its civilian atomic activities. The IAEA resolution -- worded to pass muster with Iran\'s allies Russia and China -- notably stopped short of sending the matter to the UN Security Council. Instead, it said it was \"essential for Iran and the Agency to intensify their dialogue\" and called on Tehran \"to comply fully and without delay with its obligations under relevant resolutions of the UN Security Council.\" Earlier Sunday Iran said it was ready to cooperate \"further\" with the UN atomic energy watchdog if it \"balances its approach\" to the Islamic republic, Foreign Minister Ali Akbar Salehi said on Sunday, according to the ISNA news agency. \"We are prepared to cooperate with the agency more than ever, if the (UN) agency balances its approach and complies with its statutes and the safeguard agreements,\" Salehi was quoted as saying. \"If that is the case, we are prepared to cooperate much the same as before and even further with the agency,\" he said. Libya\'s former leader was captured and killed on October 20.