NEW DELHI, Dec 4, 2025 (BSS/AFP) - Russia and India call each other "time-tested" friends with ties dating back to the Soviet era, but their relationship has come under significant pressure since Moscow's invasion of Ukraine.

US President Donald Trump has pressured India to curb purchases of Russian oil -- arguing it is fuelling Moscow's war -- and has imposed steep 50 percent tariffs on New Delhi.

The relationship comes under further scrutiny as Russian President Vladimir Putin visits New Delhi on Thursday, his first trip to India since December 2021. He last met Prime Minister Narendra Modi in September in China.

Here are five key areas of cooperation and tension:

- Oil and energy -

India emerged as a major buyer of Russian oil after the start of the Ukraine war, providing Moscow with a crucial export market as Europe sharply reduced purchases.

In 2024, Russia supplied nearly 36 percent of India's total crude imports, around 1.8 million barrels of discounted oil per day.

That saved India billions of dollars while also bolstering Moscow's war coffers, straining New Delhi's ties with Western partners, and prompting Trump to hike tariffs.

Trump has claimed that Modi has agreed to cut its Russian oil imports as part of a prospective US trade deal, something New Delhi has not confirmed.

But trade data suggests purchases have started to decline.

- Defence -

Russia remains one of India's largest arms suppliers, though New Delhi has moved to reduce its dependence by increasing purchases from the United States, France and Israel.

At the same time, India has boosted domestic production.

As a result, Russia's share of India's arms imports fell from 76 percent in 2009-13 to 36 percent in 2019-23, according to the Stockholm International Peace Research Institute (SIPRI).

A possible deal for Russia's advanced S-400 air defence systems is expected to be discussed, as well as proposals for co-production with India of Russia's Su-57 fighter jets.

India currently has three S-400 units, with delivery of two more stalled by Western sanctions.

- Trade -

Russia is India's fourth-largest trading partner, with bilateral trade hitting a record $68.7 billion in 2024-25, according to official data.

But it is far from an equal relationship: over 90 percent of that came from Indian imports from Russia, amounting to $63.8 billion, mainly fuels and oil.

India mainly exports nuclear reactors and machinery and some pharmaceuticals.

Analysts suggest a substantial volume of unofficial trade -- possibly 15-25 percent above reported figures -- moves through shadow shipping networks.

Some allege that involves strategic electronics and dual-use items to circumvent Western sanctions.

- Ukraine war -

India has walked a tightrope to avoid condemning Russia's war in Ukraine, while maintaining ties with Western nations.

When Modi and Putin met in 2022 in Uzbekistan, Modi said he wanted the war to end "as soon as possible".

Allegations that Indian citizens were duped into fighting for Russia have added to frictions.

- 'Non-alignment' -

India's long-standing policy of "non-alignment" continues to guide its approach, preserving a historical partnership with Russia while expanding ties with the United States and Europe.

Washington has regarded India as a critical partner, especially in balancing China's power.

But Modi has repeatedly emphasised a "multipolar" world order and resisted calls to distance India from Moscow.

"India seeks to maintain its longstanding relationship with Russia, which is vital not only for managing its challenging relations with China but also for its strategic autonomy -- the core principle of its foreign policy," said Praveen Donthi from the International Crisis Group.