Iran's "extensive" missile development program has allowed the country to build the "largest missile force in the Middle East," according to a new report by the U.S. Defense Intelligence Agency (DIA).

"The size and sophistication of its missile force continues to grow despite decades of counterproliferation efforts aimed at curbing its advancement," said the study, released by the Pentagon on November 19.

Despite decades of sanctions imposed on Iran's missile program, its projectile force includes ballistic missiles that could strike its regional foes at ranges of 2,000 kilometers.

"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 Iran Military Power report said.

Iran also uses unconventional warfare operations and a network of "militant partners and proxies" to enable it to advance its interests in the region and attain "strategic depth," the study said.

It added that Tehran provides financial, political, training, and material support to groups including Lebanon's Shi'ite Hizballah movement, Yemen's Shi'ite Huti rebels, and the Afghan Taliban.

"Tehran does not seek to return the Taliban to power, but aims to maintain influence with the group as a hedge in the event that the Taliban gains a role in a future Afghan government," the report said.

The study noted that Iran had remained "implacably opposed to the United States and its presence in the Middle East."

Overall, Tehran's military power buildup serves two important goals: "ensuring the survival of the regime and securing a dominant position in the region."

In an introduction to the study, DIA Director Lieutenant General Robert Ashley said Iran "sees itself as closer than ever to achieving its goals."

"By applying a rigorous lessons-learned process during decades of conflict in the Middle East, Iran has adapted its military capabilities and doctrine to account for developments by the United States and its allies. Although still technologically inferior to most of its competitors, the Iranian military has progressed substantially over the past few decades," Ashley added.

Iran would develop its defense capability faster if it were not for a UN-mandated arms embargo for most weapons that is set to expire in October 2020, the U.S. agency warned.