Russian President Vladimir Putin and Indian Prime Minister Narendra Modi are expected to sign some 20 documents and hold talks regarding a weapons deal during a scheduled October 4-5 meeting in New Delhi.

India is gearing up to finalize the purchase of high-tech S-400 Triumf surface-to-air missile defense system from Russia. As a result, the country could face U.S. sanctions should the US$5-billion weapons deal with Moscow goes through.

Last August, a Countering America’s Adversaries Through Sanctions Act (CAATSA) law, which was signed by U.S. President Donald Trump, is designed to punish Moscow for its “malign activities,” according to a CNN report. CAATSA, however, has loopholes which enables discretionary exemptions.

Australia’s Griffith Asia Institute’s Peter Layton comment that if the United States effects an exception for tactical ally India to purchase the S-400 system from Moscow, other countries – such as Turkey – should be allowed to carry out similar purchases unhindered.

“The CAATSA will appear a rather subjective sanction program if it only applies to some nations and not all,” said Layton

Last month, the Trump administration imposed sanctions on China for purchasing Russian military equipment. India and Russia have been in talks about the S-400 system since 2015.

The high-tech system is considered the most effective surface-to-air system in its class and surpasses the capabilities of the U.S. Patriot missile system.

“Apart from a conversation tete-a-tete, the sides will have talks with restricted attendance, then the talks in an extended format, and then a working breakfast as a continuation of the latter talks where ministers and leading businessmen will be present,” Putin aide, Yuri Ushakov, said.

Modi and Putin held a successful annual bilateral summit last year, followed by meetings in Astana and at the G20 in Germany prior to another meeting Sochi this year.

Before the Russian president arrived in Delhi, the U.S. State Department had urged all allies and partners to forgo transactions with Moscow that would trigger sanctions.

Modi and Putin are also expected to discuss international and bilateral issues in an informal October 4 meeting.

“Next on the itinerary is the signing of bilateral documents, and there are many of them in the portfolio,” Ushakov said. “We have 23 document at this moment and some of them are still in the phase of coordination.”