Russian President Vladimir Putin will oversee the signing of a $5 billion deal this week to supply Delhi with S-400 air defense systems, a top Kremlin aide said on Tuesday ahead of Putin's trip to India.

"The president is leaving for India on Oct. 4," Putin's top foreign policy aide Yury Ushakov told reporters.

"The key feature of this visit will be the signing of the agreement to deliver S-400 air defense systems," he said. "The value of the contract will be more than $5 billion."

Moscow has been negotiating to sell the S-400 long-range surface-to-air missiles to India for months.

The sale has irked India's defense partner Washington, which has wanted to wean India off Russian technology, and a senior Pentagon official said in August that sanctions against India would come under consideration if its purchase goes through.

India has signaled it will ask Washington for a special waiver from sanctions, though a U.S. official last week said there is no guarantee it would do so.

Earlier this year the U.S. threatened to impose sanctions over the purchase of S-400s against Turkey, which opted for the Russian-made systems after the U.S. and other NATO allies refused to sell air defense systems to Ankara.

Qatar, China and Saudi Arabia have already bought or are planning to purchase the anti-aircraft missile weapon from Russia.

The sale to Qatar has riled Saudi Arabia, which in June threatened "all necessary measures" if Russia went through with the deal with its regional rival. The sale proceedings have gone forward, however, with Doha calling the purchase its "sovereign" decision.