Iran's state shipping line is reported to renaming many of its freighters in a bid to circumvent international sanctions on arms transfers and the clandestine supply of high-tech equipment for its contentious nuclear program.

A study by the Stockholm International Peace Research Institute released Jan. 30 said the state-owned Islamic Republic of Iran Shipping Lines has renamed 90 of its 123 vessels since 2008, many with innocuous English names like "Bluebell" or "Angel." One was simply named "Alias."

SIPRI reported the company has also reflagged a "significant percentage" of its fleet to further mask its clandestine arms shipments to Tehran's allies, such as Syria, and proxies, such as Hezbollah in Lebanon.

This is also intended to confuse U.S. authorities striving to block Iran's acquisition of components and high-tech machinery for what Washington insists is a secret program to develop nuclear weapons.

Western intelligence officials say Iran has consistently used IRISL to transport nuclear components, largely bought clandestinely through front companies in the West.

"The Iranian ships are being shuffled like a deck of cards in a Las Vegas casino," observed Hugh Griffiths, SIPRI arms trafficking expert and one of the authors of the institute's report.

"There is a constant game of cat and mouse being played and the renaming and reflagging of vessels is a way of trying to avoid inspection because of sanctions."

The United States launched a crackdown on IRISL in 2008. Stuart Levey, then U.S. Treasury undersecretary for terrorism and financial intelligence, observed that Iran's merchant fleet was "a critical lifeline for Iran's proliferation and evasion. …

"Some of Iran's most dangerous cargo continues to come and go from Iran's ports, so we must redouble our vigilance over both their domestic shipping lines and attempts to use third-country shippers and freight forwarders for illicit cargoes."

SIPRI reported that the Iranian shipping companies reflagging efforts, aimed at shielding their vessels from international scrutiny, has meant that on paper the Islamic Republic's maritime fleet has shrunk dramatically.

Until 2011, IRISL was ranked the 23rd largest container line in the world. Now it's not even listed in the top 100.

In 2008, the U.S. Treasury's Office of Foreign Assets Control, invoked regulations designed to freeze the assets of proliferators of weapons of mass destruction and initiated sanctions against IRISL for working with the arms of the Revolutionary Guards Corps that oversees Iran's nuclear and ballistic missile programs.

That brought a swift response from companies around the world, which stopped dealing with IRISL.

It was then, the Financial Times reported, that the Iranian company "started to use an array of deceptive and practices to conceal its identity and skirt sanctions -- including falsifying shipping documents, changing names and nominal ownership of vessels and even repainting ships.

"It has also sought to assign vessel ownership to front companies outside Iran," the Financial Times reported.

Most of the vessels originally identified as belonging to IRISL are listed as being owned and operated by companies that don't appear on the U.S. blacklist. These companies are invariably located far from Iran, in places such as Hong Kong, Germany, the Isle of Man, Malta or Cyprus.

But in most cases, international investigators have established from corporate records that these fronts are either run by IRISL officials or are wholly owned by the Iranian company.

IRISL denies any involvement in clandestine weapons or nuclear shipments but the unmasking of its corporate camouflage efforts underline the extent of Tehran's maritime operations.

Lloyd's of London, the international shipping registry, says at least four IRISL vessels have been scuttled.

Lloyd's issues large merchant vessels with unique identifying numbers and tracks them across the globe during their operational lifetimes.

SIPRI reported that in October 2010, Germany removed ships suspected of being owned by IRISL from its shipping registry after the European Union imposed sanctions on the Iranian company.

But, the institute noted, other EU members, including Cyprus and Malta, continue to have Iranian ships on their registries.

Since the U.S. Treasury crackdown began, the United Nations has named three IRISL subsidiaries for international sanctions and granted powers to allow Iranian-flagged ships, and vessels carrying cargoes to or from Iran to be inspected.

The U.S. Treasury later sanctioned five IRISL front companies and 27 ships and identified many IRISL vessels that had been renamed.