Iran is continuing to use front companies and other concealment methods to circumvent U.N. sanctions but the bans have succeeded in slowing its nuclear and ballistic missile programs, according to a report by U.N. experts obtained Tuesday by The Associated Press.

The expert panel said sanctions have made it harder, costlier and riskier for Iran to acquire items needed for its banned nuclear and missile activities.

"At the same time, Iran's circumvention of sanctions across all areas, in particular the use of front companies, concealment methods in shipping, financial transactions and the transfer of conventional arms and related materiel is willful and continuing," the panel said. "Iran maintains its uranium enrichment and heavy water-related activities ... and in the area of ballistic missiles, continues to test missiles and engage in prohibited procurement."

It said most violations of the ban on Iran exporting conventional arms involve Syria, its neighbor and ally.

The U.N. Security Council imposed a fourth round of sanctions against Iran in June for refusing to suspend uranium enrichment and start negotiations with the U.S., Russia, China, Britain, France and Germany on its supect nuclear program.

The eight-member panel was appointed in November to assess implementation of the sanctions. Security Council diplomats said its final report to the council committee monitoring sanctions against Iran could be made public as early as Thursday.

The new sanctions target Iran's powerful Revolutionary Guard Corps, which controls companies and organizations that have links to weapons proliferation, as well as companies or organizations involved in nuclear or ballistic missile activities and linked to the government controlled Islamic Republic of Iran Shipping Lines.

In the report, the panel said the Revolutionary Guard Corps' influence on decision-making on nuclear and ballistic missile programs "is regarded as increasing through its growing political, economic and social power."

Elements of the Revolutionary Guard, known as the IRGC, are engaged in a wide range of prohibited activities, including acquiring material and technology for its nuclear and ballistic missile programs, smuggling banned material and weapons, and establishing front companies to evade sanctions, it said.

While the latest sanctions order the freezing of financial assets of 15 companies and organizations linked to the Revolutionary Guard, along with some individual guard members, the panel said this is only a "limited number" of those involved in illegal activities.

"Given the use of aliases and ease with which front companies engaged in procurement ... can be established, Iran is successfully evading the impact of sanctions designating specific IRGC entities," the panel said.

The report details nine incidents of alleged sanctions violations by Iran including the NATO-led force's seizure of an ammunition shipment from the IRGC to the Taliban in February in Nimruz province, Afghanistan, and Israel's seizure of three crates of arms bound from Syria to Egypt in March.

After an investigation, the panel concluded that Iran attempted to illegally transfer 13 containers of ammunition to West Africa, which were intercepted by Nigerian authorities last October.

It said two Revolutionary Guard front companies played key roles — Behineh Trading Company and International Trading and General Construction — and called on the Security Council to impose sanctions on both companies as well as two individuals.

It also urged the council to seek additional information on two shipping companies affiliated with Iran Shipping Lines with a view to imposing sanctions against them.

"Overall, the panel has found that sanctions are constraining Iran's procurement of items related to prohibited nuclear and ballistic missile activity and thus slowing development of these programs," the panel said.

But while slowing Iran's nuclear program, it said sanctions are "not yet having an impact on the decision calculus of its leadership with respect to halting uranium enrichment and heavy water-related activities."

The report said Iran may be seeking additional supplies of natural uranium both for the planned heavy water reactor in Arak or an expansion of its ongoing enrichment activities, the report said.

Nonetheless, the panel said, "sanctions have clearly forced changes in the way in which Iran procures items."

"Iran is increasingly seeking technologies and know-how to improve its indigenous production capabilities in the nuclear area," the report said. "These are not items found on specific control lists ... but that improve Iran's ability to produce controlled items indigenously."

One example, the panel said, is a shipment of rolls of "phosphor bronze mesh wire," seized by South Korean authorities in February. It concluded that the wire could be used in Iran's heavy water research reactor, which is under construction.

It said Iran is also seeking to purchase equipment not on control lists that can be used to produce material and spare parts for its ballistic missile program.

The panel cited its inspection of 302 drums of aluminum powder being shipped to Iran from China and intercepted by Singaporean authorities in January. It can be used in paints and plastics but the report said it would also produce 100 tons of rocket propellant.

While U.N. member states are taking a more active role in implementing sanctions by strengthening export controls, watching financial transactions and monitoring port and customs activities, the panel lamented that only 66 of the 192 U.N. member states have submitted required reports on measures they are taking to implement the latest sanctions against Iran.