Defense Secretary Jim Mattis is arguing for waivers to let US allies and partners avoid sanctions for buying Russian arms. The move could include giving Turkey and India a pass on the purchase of advanced S-400 anti-air defense systems.

At a Senate Armed Services Committee hearing Thursday, Mattis said "national security exceptions" must be made to the Countering America's Adversaries Through Sanctions Act (CAATSA) in the long-term interests of the US.

"There are nations in the world who are trying to turn away from formerly Russian-sourced weapons and systems," he said.

Those same nations, he said, currently need to keep the Moscow supply line open to replenish their legacy systems.

"We only need to look at India, Vietnam and some others to recognize that eventually we're going to penalize ourselves" in the future by strict adherence to CAATSA, Mattis said.

Defense Secretary Jim Mattis with Indonesian Minister of Foreign Affairs Retno Marsudi at the Foreign Ministry in Jakarta, January 22, 2018. Thomson Reuters

He pointed to Indonesia, which has become increasingly vital to the Trump administration's overall South Asia strategy.

"Indonesia, for example, is in the same situation — trying to shift to more of our airplanes, our systems, but they've got to do something to keep their legacy military going," Mattis said.

CAATSA was passed by Congress last year to punish Russia for its invasion of Crimea, support of separatists in Ukraine, and involvement in Syria. President Donald Trump, who had doubts about the Russia sanctions, reluctantly signed the bill last August.

Mattis called on Congress to include "national security exceptions" in the National Defense Authorization Act for fiscal 2019 but acknowledged that Russia's sale of the S-400 systems is "causing a lot of concern."

The Russian S-400 Triumf, also known by its NATO codename of SA-21 Growler. NOSINT

Russian President Vladimir Putin was in Ankara earlier this month to firm up the proposed $3 billion sale of the S-400 systems, billed as "F-35 killers," to NATO ally Turkey.

The US and NATO allies have warned Turkey that the S-400s are not compatible with other NATO systems, but Turkish President Recep Tayyip Erdogan has pressed on with the deal.

Last week, State Department Assistant Secretary Wess Mitchell told the House Foreign Affairs Committee that Turkey is risking sanctions under CAATSA, adding that it could also be cut off from buying the F-35 Joint Strike Fighter.

India is also in the final stages of a potential $5 billion to deal for the S-400s, dubbed the Sa-21 Growler by NATO. India began bargaining with Russia on S-400 sales after regional rival China signed off on its own purchase of the S-400 systems.