India's Financial Crimes Agency has arrested prominent opposition politician and Delhi Chief Minister Arvind Kejriwal, his party said.
The arrest is linked to corruption allegations related to the city's policies on alcohol sales.
Kejriwal and his Aadmi Party deny any wrongdoing and say the case is politically motivated.
His arrest comes weeks before the start of voting in the country's general elections.
Police surrounded Mr Kejriwal's house on Thursday while it was searched by members of the Enforcement Directorate agency.
The case relates to allegations that the alcohol sale policy implemented by the Delhi government in 2022 – which ended the government monopoly – gave undue advantages to private sector retailers.
Mr. Kejriwal has ignored several subpoenas in this case.
The association accused the ruling Bharatiya Janata Party of “dirty politics” and said it would seek an urgent hearing in the Supreme Court to secure Mr Kejriwal's release.
Before the vote, opposition parties accused Prime Minister Narendra Modi's government, the Bharatiya Janata Party, of misusing government agencies to achieve political goals.
Dilip Pandey, a RJD MP and speaker of Delhi Parliament, told the BBC that the arrest showed Modi was “afraid of Kejriwal”.
“They can arrest Kejriwal but not his ideas. We will continue to fight his arrest and the unfair policies of Mr. Modi's government,” Pandey said.
They are among several prominent opposition leaders who are the subject of criminal investigations that many say are politically motivated.
Rahul Gandhi, the most prominent member of the opposition Congress party, was found guilty of criminal defamation last year following a complaint filed by a BJP member.
His two-year prison sentence disqualified him from membership of Parliament for some time until the sentence was suspended by a higher court, but this raised concerns about the state of democracy in India.
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