A bipartisan team of lawmakers is warning that Russia’s decision to arm Iran with advanced missile systems will erode America’s ability to launch a military strike against the Islamic Republic’s contested nuclear sites, according to a letter sent Monday to the Obama administration.

Russia announced Monday that it will reverse a years-long ban on arming Iran with the advanced S-300 air defense missile system. The move was condemned by the Obama administration, which had viewed the ban as a sign of its successful attempts to rein in Russian proliferation.

Iran says the S-300 system could arrive as soon as later this year.

Leading lawmakers are now warning that the S-300 system would significantly boost Tehran’s defense capabilities and help it protect its sensitive nuclear sites from any potential military strike by the United States.

"Maintaining a credible military threat is a necessary component to prevent Iran from obtaining a nuclear weapons capability," Reps. Peter Roskam (R., Ill.) and Ted Deutch (D., Fla.) wrote on Tuesday to Secretary of State John Kerry, according to a copy of the letter obtained by the Washington Free Beacon.

"Allowing the Iranian regime to acquire this advanced system could significantly impact our ability to take military action against Iran, should this become necessary," the lawmakers said.

Roskam and Deutch maintained that Russia’s sale of the S-300 system to Iran "will significantly enhance Tehran’s military capabilities and threaten to further destabilize the region," which is already roiled in conflict.

The sale complicates efforts to strike a nuclear agreement with Iran. Russia has been a key U.S. ally in pushing for Tehran to roll back its program.

"This news is particularly concerning in light of ongoing nuclear negotiations with the Islamic Republic of Iran and casts further doubts on Russia’s role as a constructive partner in this process," the lawmakers wrote.

Roskam and Deutch have repeatedly expressed concerns about the sale and have petitioned the Obama administration to take action since 2013.

Secretary of State John Kerry phoned his Russian counterpart after the announcement Monday to express his concerns over the matter.

Both the White House and the State Department outlined their concerns during briefings with reporters.

A senior congressional aide familiar with the issue said the S-300 system is an advanced piece of hardware that would boost Tehran’s defense.

"This is not just about preventing any arms to Iran," the aide said. "This is about stopping the flow of anti-aircraft missiles that would potentially enable Tehran to fend off an attack on its illicit nuclear and military facilities."

"For years, this administration has said that all options remain on the table when it comes to stopping Iran from acquiring a nuclear weapons capability," the source said. "Failing to stop a transfer of S-300s from Russia to Iran may not only make a military strike less viable, but take this option off the table altogether."

In 2010, the Obama administration described the sale of S-300s to Iran as a so-called red line but has declined to explain its stance in light of Monday’s announcement.