Bandi Sanjay Kumar's supporters protested his detention.
Bandi Sanjay Kumar, the president of the BJP in Telangana, was taken into custody by the police on Tuesday night, setting off a political firestorm and drawing criticism from the party's top leadership in New Delhi. He has been sent to a two-week judicial custody.
Mr Kumar, a member of parliament from Karimnagar district, was taken into custody from his home without any explanation, according to his party colleagues. He was later moved to various police stations in different districts, raising questions about his whereabouts and safety.
Calling it a case of "illegal arrest", the BJP also filed a petition in the Telangana High Court on Wednesday, seeking to know the grounds for Mr Kumar's detention and his current location.
In a First Information Report (FIR) released amid the spiralling outcry, the police said Mr Kumar had been taken into "preventive detention". He was later arrested over the leak of secondary school exam papers, a charge that his party has dismissed as baseless and politically motivated.
The police action came amid heightened tensions between the BJP and the ruling Bharat Rashtra Samithi, or BRS, ahead of Prime Minister Narendra Modi's visit to the state on Saturday. PM Modi is expected to inaugurate several development projects and address a public rally.
Mr Kumar, who has been vocal in his criticism of the BRS government and its chief minister, K Chandrasekhar Rao, was picked up from his residence late on Tuesday night. Video footage showed him being dragged by policemen and forced into a van outside. His supporters tried to resist the arrest and clashed with the police.
The BJP's national leaders condemned the detention of Mr Kumar and demanded his immediate release. G. Kishan Reddy, a union minister and a senior BJP leader from Telangana, called it an "undemocratic" act that violated Mr Kumar's fundamental rights.
Amit Malviya, the head of the BJP's information technology department, said on Twitter that the arrest was an attempt by Mr Rao to "intimidate" the opposition and "muzzle" dissent.
"In a midnight operation, Telangana police has arrested BJP state President Bandi Sanjay Kumar on fabricated charges of being involved in a secondary school paper leak. This won't end well for KCR," Mr Malviya wrote, using Mr Rao's initials.
Hundreds of BJP workers staged protests outside various police stations where Mr Kumar was reportedly taken. They raised slogans against Mr Rao and the BRS government and accused them of misusing their power to suppress the opposition.
The BJP, which has been trying to expand its base in Telangana, a southern state that was carved out of Andhra Pradesh in 2014, sees Mr Rao as its main rival and has accused him of corruption, nepotism and minority appeasement.
The party won four parliamentary seats in Telangana in the 2019 general elections and made further gains in the local elections last year. It hopes to challenge the BRS, which has been in power since 2014, in the next state assembly elections due this year.