The United States tripled weapons exports last year, mostly to allies in the Middle East in a major drive to counter Iran's ambitions in the region, a new study for the U.S. Congress said Monday.

The study by the non-partisan Congressional Research Service, a division of the Library of Congress, said U.S. weapons exports totaled $66.3 billion in 2011, out of a global weapons market of $85.3 billion.

By contrast, Russia's arms exports stood at a distant second at $4.8 billion in the same year.

The study said the 2011 figures for U.S. arms exports constituted an "extraordinary increase" in just one year over the $21.4 billion in 2010 sales. The U.S. exported weapons worth $31 billion in 2009.

Saudi Arabia, the United Arab Emirates and Oman were major buyers of U.S. weapons at record levels last year, the study said.

In addition, the U.S. had worked out a policy goal with Arab allies in the Gulf to build a regional missile defense system to protect cities, oil refineries, pipelines and military bases from possible Iranian military attack.

In agreements with the U.S. worth 33.4 billion dollars last year, Saudi Arabia agreed to buy 84 advanced F-15 fighters, ammunition, missiles and logistics support and pay for upgrading 70 of the F-15s. The U.S. also sold military equipment that included dozens of Apache and Black Hawk helicopters to the Saudis.

The UAE purchased a Terminal High Altitude Area Defense and an advanced antimissile shield, which includes radars, which were valued at $3.49 billion, as well as 16 Chinook helicopters for $939 million.

Oman bought 18 F-16 fighters for $1.4 billion, the study said.