Indian Prime Minister Narendra Modi's party on Saturday regained power in the nation's capital for the first time in 27 years, a boost for the Hindu-nationalist leader after a disappointing national election last year.

Modi's Bharatiya Janata Party won 48 of the 70 seats in the Delhi capital district, well ahead of the 22 for the opposition Aam Aadmi Party (AAP) of Arvind Kejriwal, a fierce critic of Modi, data from the Election Commission of India showed.

"It is our guarantee that we will leave no stone unturned in developing Delhi, improving the overall quality of life for the people," Modi wrote on social media platform X.

AAP, which grew out of an anti-corruption movement in 2012, tasted its first electoral success in Delhi and has ruled the territory, which includes India's parliament and federal government offices in New Delhi, for two terms from 2015.

Kejriwal, 55, an anti-corruption crusader-turned-politician who was arrested on graft charges weeks before last year's general election began, alleged a political vendetta by the Modi government. The BJP denies his claims. 

Kejriwal, who was released on bail and resigned as Delhi chief minister to focus on campaigning for the state election, lost the seat he was contesting.

AAP will play the role of constructive opposition after trying to improve the city's infrastructure, education, and healthcare in the past ten years, Kejriwal said in a video message on X.

AAP, which won the past two elections with thumping majorities, was popular because of its largesse, such as free water and power for the poor, its main voter base.

To counter AAP, the BJP promised monthly payments of 2,500 Indian rupees ($28) to all poor women, a one-time payment of 21,000 rupees to each pregnant woman, subsidised cooking gas, a monthly pension of 2,500 rupees for the elderly and 15,000 rupees for the youth to prepare for competitive exams.

Modi lost his majority in India's parliament last year but returned as prime minister for a record-equalling third term with the support of regional parties. His BJP has won three of four subsequent state elections.

State election victories help political parties boost their numbers in the upper house of parliament, which is key for decision-making.