Two U.S. senators have urged President Joe Biden to waive sanctions against India over its purchase of Russia's S-400 air defense system, saying such a punitive measure would endanger growing cooperation, Reuters reports.

India signed a $5.5 billion-dollar deal with Russia in 2018 for five of the surface-to-air missile systems.  However, the deal caused friction with the United States which, in 2017, passed a law stating that any country that collaborates with the defense and intelligence sectors of Russia could face sanctions.

Republican Senator John Corny and Democrat Senator Mark Warner wrote a letter to President Biden calling for a waiver on the grounds of national security and broader cooperation.

The senators added that they were concerned that the transfer of the Russian systems would trigger sanctions against India

India has made a down payment on the S-400s, and the first set of missile batteries is expected to begin to be deployed at the end of this year.