India is planning to buy five S-400 Triumf missile air defence systems from Russia.

Highlights The signing will be overseen by Vladimir Putin, who will visit New Delhi

The agreement's signing will be the key feature of Putin's India visit

The value of the contract will be more than $5 billion, Putin's aide said

India and Russia will sign a deal for the multi-billion-dollar S-400 surface-to-air missile system this week. The signing of the deal for Moscow's most advanced air defence system will be overseen by Russian president Vladimir Putin, who is visiting New Delhi on October 4-5 for the annual India-Russia summit, a top Kremlin official said.

"The key feature of this visit will be the signing of the agreement to deliver S-400 air defence systems," Vladimir Putin's top foreign policy aide Yury Ushakov said, according to news agency AFP.

"The value of the contract will be more than $5 billion," Mr Ushakov added.

The US had last month warned against the deal, saying it would be considered as a "significant transaction" and has a potential for imposing tough US sanctions.

US President Donald Trump had last month signed an executive order, paving the way for slapping crippling sanctions on countries and foreign entities and individuals violating the Countering America's Adversaries Through Sanctions Act (CAATSA).

After signing of the order, the US imposed sanctions on China, an Equipment Development Department under China's Ministry of Defence and its director Li Shangfu for its recent purchase of Russian Sukhoi Su-35 fighter jets and S-400 surface-to-air missile.

India is planning to buy five S-400 Triumf missile air defence systems from Russia. The S-400 missile system, which has been in service since 2007, can track some 300 targets and shoot down around three dozen targets simultaneously over a range of 400 kilometres. The sensitive radars of the system are thought to be able to detect even stealth aircraft which present a very small radar cross-section and are often impossible for other systems to track.

A separate deal to supply four frigates to India may also be signed during Putin's visit.