Despite decades of sanctions, Iran has succeeded in developing its missile arsenal, which is larger than that of any other Middle Eastern country including Israel, a Pentagon study said Tuesday.

"Iran has an extensive missile development program, and the size and sophistication of its missile force continues to grow despite decades of counterproliferation efforts aimed at curbing its advancement," the Defense Intelligence Agency said.

The study said Iran considered missiles to be a strategic necessity due to the limitations of its air force, which still has some US planes ordered by the pro-Western shah, who was toppled in 1979.

"Lacking a modern air force, Iran has embraced ballistic missiles as a long-range strike capability to dissuade its adversaries in the region - particularly the United States, Israel and Saudi Arabia - from attacking Iran," the report said. Iran has "the largest missile force in the Middle East," the report said. A US intelligence official said on condition of anonymity that the assessment included Israel.

The report said that Iran had developed a series of missiles that could strike at a distance of 1,250 miles (2,000 kilometers) - capable of reaching Israel or Saudi Arabia.

Iran in 2017 showcased the 1,250-mile-range Khoramshahr missile, which can carry multiple warheads. The Pentagon study, in line with a tweet at the time by President Donald Trump, said the missile appeared to use technology from North Korea.