India's Prime Minister Narendra Modi congratulated Pakistani counterpart Shehbaz Sharif on Tuesday for his return to the premiership, a rare expression of goodwill between leaders of the two nuclear-armed rivals.

Sharif was officially sworn in Monday as prime minister for a second time after a poll marred by claims of widespread vote rigging.

The 72-year-old's army-backed Pakistan Muslim League-Nawaz (PML-L) has formed a coalition government with their historic rival the Pakistan Peoples Party (PPP) and several smaller factions that shuts out loyalists of jailed former prime minister Imran Khan, who won the most seats.

"Congratulations to @CMShehbaz on being sworn in as the Prime Minister of Pakistan," Modi said in a post on social media platform X.

India and Pakistan are bitter adversaries with longstanding political tensions.

The two nations have fought three wars and numerous smaller skirmishes since being carved out of the subcontinent's partition in 1947.

But Sharif is seen in India as more conciliatory toward New Delhi than his predecessor Khan.

Unusually for a senior Pakistani politician, Sharif visited India in 2013 when he was chief minister of Pakistan's influential Punjab province.

He visited his family's ancestral village on the Indian side of the frontier and met with then-prime minister Manmohan Singh in New Delhi, along with other officials.

Modi also attended a Sharif family wedding during a surprise trip to Pakistan in 2015, a year after the Hindu nationalist leader took office.

He was hosted by Sharif's elder brother Nawaz, himself prime minister at the time.

Hindu nationalist sentiment has risen in India under Modi, a populist leader seeking a third term in office in general elections expected from April.

The two countries downgraded their diplomatic ties during Khan's premiership in 2019 after a dispute over India's attempt to entrench its grip over the part of Kashmir it controls.

The Himalayan region, home to a long-running and deadly insurgency against Indian rule, is divided between the two countries and claimed by both in full.