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The minister was arrested this morning after hours of questioning in connection with a money laundering case.
The case is linked to alleged siphoning of money during the AIADMK government led by former Chief Minister J Jayalalithaa. Mr Balaji, then in the AIADMK, was the transport minister in the Jayalalithaa government
He had been taken to the hospital for a medical check-up by the ED after he complained of chest pain. Doctors at the Chennai hospital said the angiogram revealed a triple-vessel disease.
Mr Balaji had broken down on the way to the hospital. Visuals of him weeping in the ambulance and while being wheeled into the hospital, were widely circulated.
"He is in the ICU. He was unconscious and did not respond when he called him by his name. There is a swelling near his ear, doctors say there is variation in his ECG (electrocardiogram)... these are symptoms of torture," DMK leader PK Sekar Babu said.
Mr Balaji's wife has filed a petition in the Madras High Court, alleging he was arrested without any notice or summons. The court has agreed to an urgent hearing.
The ruling DMK has alleged the minister's arrest is a BJP plot. "We would face it legally. The DMK will not be cowed down by the BJP's intimidation," said Tamil Nadu Sports Minister and DMK Youth Wing chief Udhayanidhi Stalin.
Tamil Nadu Chief Minister MK Stalin, who visited Mr Balaji at the hospital, slammed the BJP-led central government. Accusing the party of "politics of intimidation", he said the raids on Mr Balaji were a "violation of (the country's) federal structure".
On Tuesday, the ED raided Mr Balaji's home and office at the Tamil Nadu Secretariat and the premises of his brother and a close aide in Karur district.
The Income Tax authorities had searched the properties of Mr Balaji's associates after the Supreme Court allowed the Enforcement Directorate to continue its investigation into cash-for-jobs allegations against him.
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