At least 81 US aircraft have been lost since Washington and Israel started their war against Iran in late February, a report prepared for US lawmakers concludes.

The cost of destroyed or damaged American warplanes, helicopters, and drones could reach $3.3 billion, according to the paper released by the Congressional Research Service (CRS) on Tuesday.

The figures provided in the document are based on news reports and statements by the US Central Command and officials from the War Department, the CRS said. Congress previously criticized the Pentagon for its reluctance to provide a complete list of aircraft losses in the conflict.

Some of the most advanced US warplanes have suffered hits, including one F-35A Lightning II stealth fighter, which was damaged by Iranian fire on March 19, and 12 F-15E Strike Eagle fighters, the report read.

Three F-15s were shot down by friendly fire in Kuwait’s airspace in early March and another was hit over Iran the next month. Eight more suffered minor damage during Tehran’s missile attack on an airbase in Jordan in September, but have since been fixed and returned to service, the CRS said.

Seven KC-135 Stratotanker aerial refueling aircraft were also destroyed or damaged, according to the paper. Two were involved in an incident on March 14, with one KC-135 crashing in Iraq, killing all six crew members, and another performing an emergency landing. Six more refueling planes were affected in an Iranian bombardment of a US base in Saudi Arabia a few days later.

Other notable aircraft losses included two A-10 Thunderbolt IIs, two MC-130J special operations aircraft and an E-3 Sentry airborne warning-and-control aircraft, the report added.

Among the helicopters reported destroyed, one AH-64 Apache was shot down over the Strait of Hormuz, four AH-6 Little Birds were lost during rescue operations and an MH-60 Sea Hawk crashed over the Arabian Sea in mid-September.

The heaviest attrition was felt by the US fleet of MQ-9 Reaper drones, with at least 45 lost during the conflict with Iran, the report read.

The CRS said that several issues could benefit from congressional oversight, including whether the Pentagon possesses the funding to replace damaged aircraft and whether the losses of aging platforms, which are in short supply, could create capability gaps for the US military.

Last month, the Congressional Budget Office (CBO) said that the conflict with Iran had cost the US approximately $38 billion in its first five months. The bill could increase by another $2 billion to $3 billion for every additional month of fighting, it cautioned.

Iran has increased its capacity to produce arms by 2.5 times compared to its pre-war level, the country’s Defense Ministry spokesman, Brigadier General Reza Talaei-Nik, said on Tuesday, warning that any further US aggression will be met with a decisive response by Tehran. The Islamic Republic currently manufactures more than 1,000 types of weapons systems and munitions, many of which have undergone technological upgrades during the conflict, he stressed.