Russian President Vladimir Putin welcomed Indian Prime Minister Narendra Modi at the Kremlin for an informal dinner, as India and Russia eye nuclear and military deals worth billions of dollars. (Reuters)

Russian President Vladimir Putin and Indian Prime Minister Narendra Modi on Thursday pledged closer ties between their historically allied countries as their governments signed agreements in the defense, nuclear and energy sectors.

Indian and Russian officials vowed to ease visa regulations, to cooperate on a joint venture to build military helicopters in India, and to develop nuclear reactors in India.

But while Modi and Putin exchanged warm words during the Indian leader’s visit, with Modi saying he and Putin had a “high convergence in our positions on global issues,” their joint statement notably contained no mention of a highly anticipated deal: the sale of billions of dollars in state-of-the-art Russian S-400 surface-to-air missiles.

The deal would have been the most important arms sale by Russia in more than a decade. India has imported close to $5 billion in Russian arms annually in a close partnership that stretches back to the Cold War, and the country’s Defense Acquisition Council had reportedly approved the missile deal.

Russian President Vladimir Putin and Indian Prime Minister Narendra Modi arrive for a meeting with Russian and Indian businessmen at the Kremlin. (Alexander Nemenov/AFP via Getty Images)

Although the sale was not explicitly addressed publicly on Thursday, however, it did not seem that it was off the table entirely.

Reliance Defense, an Indian arms firm, said Thursday that it signed a manufacturing and maintenance deal worth about $6 billion with the Russia’s Almaz-Antey, which produces the S-400 surface-to-air missiles.

In a statement, Reliance Defense said that “the two sides identified the air defense missile systems . . . radars and automated control systems as areas of partnership.”

Exports of Russian weapons have increased over the past several years and have become an increasingly important source of foreign currency to the Kremlin as oil prices have plummeted. While Russia has been concerned about selling defense technology to potential military rivals or countries that can copy the know-how, such as China, India has been seen as a comparatively acceptable buyer.

“India might be the only country where there are no limits on sales from Russia,” said Alexander Khramchikhin, deputy director of the Moscow-based Institute for Military and Political Analysis. “It is the only country where there is no potential for conflict with Russia.”

Khramchikhin said interest in Russian arms has grown because of the military’s adoption of new technology such as the S-400 missile systems, as well as the deployment of Russian arms, including cruise missiles, in combat in Syria.

“If arming yourself with the weapons is good publicity, then the best is actually using them in combat,” he said in a telephone interview on Thursday.

The close defense partnership between Russia and India goes back decades, and Moscow enjoyed a near-monopoly on arms sales to India shortly before the Soviet Union’s fall.

“We do things with Russia and Russia does things with us which we don’t do with any other country,” Indian Foreign Secretary Subrahmanyam Jaishankar told reporters this week. He called Russia “a very old and trusted partner.”

But in the past several years, the United States has competed with Russia to become India’s largest arms supplier, primarily through sales of military aircraft and helicopters. In September, India signed a contract to buy 15 Chinook heavy-lift and 22 Apache attack helicopters from the United States for $3 billion.

“India has decided to put its eggs in many baskets, rather than just the single Russian basket,” said Sushant Singh, an associate editor at the Indian Express newspaper who specializes in defense matters. “This is very clearly understood and accepted by Russia. They know they are no longer our only partner.”

The most important defense deal reached with Russia on Thursday was the approval of the joint manufacture of Kamov 226 helicopters, the first project for a major defense platform under Modi’s “Make in India” program.

Last year, Modi spoke of his dream to turn India from the largest arms importer to a weapons exporter.

“We dream of making India strong enough to export defense equipment to the world,” he said in public remarks. “Instead of having to import every little defense hardware, we want India to become an exporter of these equipment over the next few years.”

Lakshmi reported from New Delhi.

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