India's opposition on Wednesday stepped up pressure on the government to condemn the Russian invasion of Ukraine, a day after an Indian student died during shelling in the eastern city of Kharkiv.

India is yet to criticise long-standing arms supplier Russia publicly, instead urging both sides to cease hostilities, causing frustration among its other allies including the United States.

Thousands of Indian students remain trapped in Ukraine, leading to calls for the government to step up pressure on Russia to assist evacuation efforts.

“The government of India should stop its verbal balancing act and sternly demand that Russia stop immediately the bombing of key cities in Ukraine,” said P. Chidambaram, a lawmaker from the opposition Congress party, in a tweet.

India abstained in a United Nations Security Council vote condemning the invasion last week, though in recent days it has subtly shifted tone.

Indian Prime Minister Narendra Modi “stressed upon the importance of respecting the sovereignty and territorial integrity of nations” during a call with Polish president Andrzej Duda, a statement by India's foreign ministry said late on Tuesday.

In addition, India has taken a critical stand privately with Russian president Vladimir Putin, an Indian foreign ministry source said.

Russia has long supported India internationally on critical issues including Indian Illegally Occupied Jammu and Kashmir (IIOJK), as well as provided the bulk of its military capability.

Read: Putin lauds India as 'great power' as military, energy ties bolstered

New Delhi has for decades attempted to lessen its reliance on Russian-made weapons, while keeping the relationship close enough to avoid Moscow aligning more with rival Asian power China.

“India is increasingly uncomfortable with the position that Russia has taken, but it is very difficult for it to voice it in public,” said Harsh Pant, a defence and geopolitical analyst at the New Delhi-based Observer Research Foundation.

Some 60 per cent of India's military hardware is still Russian-made, Pant said, and a relationship with Moscow is essential to maintain equipment and source spare parts.