Arvind Kejriwal tweeted that Manish Sisodia is "innocent"
Delhi Chief Minister Arvind Kejriwal called the arrest of his deputy Manish Sisodia "dirty politics" and warned that "people will respond".
The Central Bureau of Investigation (CBI) arrested Mr Sisodia, who is also Delhi's Finance and Education Minister, after questioning for eight hours on Sunday in the Delhi liquor policy case.
"Manish is innocent. His arrest is dirty politics. There is a lot of anger among the people due to the Mr Sisodia's arrest. Everyone is watching. People understand everything. People will respond to this. This will boost our spirit further. Our struggle will get stronger," Mr Kejriwal tweeted.
"Manish Sisodia has worked very hard to ensure children from every poor home can go to school. He is an honest, decent man. But they have arrested him today. They arrest good people and patriots, while their friends loot millions from banks," Mr Kejriwal told reporters.
Mr Sisodia and others face corruption allegations in bringing a new liquor sale policy in the national capital. Lieutenant Governor VK Saxena had ordered the CBI probe last year. The Delhi government reverted to the old liquor policy and blamed the Lieutenant Governor for loss of revenue worth crores of rupees.
The BJP said the Delhi government went back to the old liquor sale policy to cover up corruption in the excise department held by Mr Sisodia.
The CBI said Mr Sisodia has not been cooperating with investigators.
AAP MLA Atishi, however, said the BJP is "afraid" of Mr Kejriwal and Mr Sisodia's rise. "The AAP's increasingly popularity is the reason behind the arrest. The BJP is trying to finish off the AAP. The case is a false one," Atishi told reporters in Delhi.