Russia has formally offered its S-400 Surface-to-air missile systems for $6 billion to India.

A deal is likely to be signed within the next few weeks, the sources add. Russia could also commence delivering the S-400 missile defense system to China by the end of the year.

Russia and India were expected to sign an agreement on the sale of the systems in December 2015 when Indian Prime Minister Narendra Modi visited Moscow for an annual summit.

Sources close to the situation tell RBTH that differences on the price held back the signing of an agreement.

The S-400 Triumf , previously known as S-300PMU-3, is an anti-aircraft weapon system developed by Russia’s Almaz Central Design Bureau in the 1990s as an upgrade of the S-300 family. It has been in service with the Russian Armed Forces since 2007.

The S-400 uses three different missiles to cover its entire performance envelope. These are the extremely long range 40N6, long range 48N6 and medium range 9M96 missile.