The Pentagon said on Thursday it plans to sell Washington's Gulf allies Saudi Arabia and the United Arab Emirates $10.8 billion worth of missiles and munitions, including "bunker-buster" bombs.
The move follows a series of US weapons deals in recent years that have bolstered the air power and missile arsenals of Gulf states, which view Iran as a menacing rival with nuclear ambitions.
The pending sale comes as the United States and five other major powers pursue high-stakes diplomacy on Iran's disputed nuclear program, with talks this week portrayed as positive by both sides.
Officials said the Defence Department notified Congress this week of the planned deal that will provide a thousand bunker-buster GBU-39 bombs to the Saudis and 5,000 to the UAE.
The sale will also include sophisticated air-launched cruise missiles that can hit targets from a long distance.
The weapons are designed for use by US-made F-15 and F-16 fighter jets previously purchased by Saudi Arabia and the UAE, according to the Defence Security Cooperation Agency (DSCA).
In 2010, Israel bought the same bunker-buster "precision-guided glide bombs," fueling speculation that it was preparing for potential pre-emptive air strikes against underground nuclear sites in Iran.
The proposed sales "will contribute to the foreign policy and national security of the United States" by improving the security of friendly countries that remain forces for "stability," the DSCA said.
Under the arms package, the Saudis were due to receive $ 6.8 billion in weapons, parts, training and logistical support.
The Saudis and the UAE will purchase hundreds of Standoff Land Attack missiles, or SLAM-ERs, and Joint Standoff Weapons (JSOW).
These advanced missiles that will enable their warplanes to hit radar installations and other targets from beyond the range of air defence systems.
The Saudis will purchase 650 of the Boeing-manufactured SLAM-ERs and 973 Joint Standoff Weapons, made by Raytheon, as well as other missiles.
The United Arab Emirates is due to buy $ 4 billion worth of weaponry, including the bunker-buster bombs, 300 SLAM-ERs and 1,200 JSOW missiles.
"The UAE continues host-nation support of vital US forces stationed at Al Dhafra Air Base and plays a vital role in supporting US regional interests," the DSCA said.
"This proposed sale will improve the UAE's military readiness and capabilities to meet current and future regional threats, reduce the dependence on US forces in the region, and enhance any coalition operations the US may undertake."
The arms sale is expected to prompt renewed criticism from human rights groups and opponents of rulers in both Gulf states, which have cracked down on internal dissent and backed repression by Egypt's military-backed leadership.
The United States recently scaled back its military assistance to Egypt in the wake of a military coup that ousted the country's first democratically elected president, Mohamed Morsi.
Congress has 30 days to block the sale but most lawmakers have endorsed previous weapons deals with the Gulf countries.