U.S. investigators are looking into a suspected arms deal between the Islamic Republic of Iran and the Libyan government of Moammar Gaddafi involving hundreds of artillery shells designed to deliver weaponized chemical agents, according to a Washington Post exclusive published late Sunday.

The shells in question -- found filled with the powerful vesicant chemical warfare agent mustard gas -- were discovered by Libyan revolutionary fighters in central Libya earlier this month. The chemical weapon's sites are currently under 24-7 surveillance by U.S. drones, officials said.

From the Washington Post:

“We are pretty sure we know” the shells were custom-designed and produced in Iran for Libya, said a senior U.S. official, one of several who spoke on the condition of anonymity because of the sensitivity of the accusation.

A U.S. official with access to classified information confirmed that there were “serious concerns” that Iran had provided the shells, albeit some years ago.

In recent weeks, U.N. inspectors have released new information indicating that Iran has the capability to develop a nuclear bomb, a charge Iranian officials have long rejected. Confirmed evidence of Iran’s provision of the specialized shells may exacerbate international tensions over the country’s alleged pursuit of weapons of mass destruction.

The discovery of weaponized mustard gas directly contradicts Gaddafi's promise to the United Nations in 2004 to dismantle the dictator's chemical weapons arsenal.

International investigators and human rights activists are concerned that chemical weapons were used against revolutionary fighters during Libya's recent conflict.

Read the full story here.