WASHINGTON — India risked U.S. sanctions when it agreed to a $5 billion deal to buy Russian missile systems. But two months after India signed the pact, it's not clear whether the Trump administration will issue a waiver or follow through with any penalties.

India's purchase of the Kremlin's S-400 Triumf surface-to-air missile system is subject to potential U.S. sanctions under the Countering America's Adversaries Through Sanctions Act, a measure that was signed by President Donald Trump in 2017.

The deal and possible sanctions could come up this week, when India's defense minister, Nirmala Sitharaman, holds talks with Defense Secretary James Mattis. The U.S. Defense chief stressed on Monday that this wouldn't be the first time India has purchased weapons from the Kremlin.

"India has been spent many, many years in its nonaligned status, and it's drawn a lot of weapons from Russia," Mattis told reporters at the Pentagon ahead of Sitharaman's arrival Monday. She is slated to leave Washington on Tuesday.

"We are here today to talk about all the issues that bring us closer together and we'll sort out all those issues here today and in the days ahead," he added, when asked about India's S-400 purchase.

Russia's S-400 system, a mobile long-range surface-to-air missile system, made its debut on the world stage in 2007. The platform rivals Lockheed Martin's THAAD, or terminal high altitude area defense, system and Raytheon's Patriot system.

Compared with U.S. systems, the Russian-made S-400 is capable of engaging a wider array of targets, at longer ranges and against multiple threats simultaneously.

What's more, the Russian-made platform costs approximately $500 million, whereas a Patriot Pac-2 battery costs $1 billion and a THAAD battery rings in at about $3 billion, according to people with firsthand knowledge of a U.S. intelligence assessment.

About 13 countries have expressed interest in buying the S-400. China, India and Turkey have already signed purchase agreements for the missile platform.

China is in the middle of receiving its final shipment of the S-400 system. Turkey, a NATO ally, is slated to receive its S-400 next year and is expected to have the system ready for use by 2020.