However, jail authorities said that they did not get any information from Jagan about his fasting.
"He (Jagan) has not given us any representation on his fast. He has to give in writing and inform, but so far there is no intimation," Chanchalguda jail superintendent B Saidaiah told PTI.
"There is no written communication/letter informing the authorities on which grounds he was resorting to the hunger strike," Saidaiah said adding the Kadapa MP, however, refused to take his breakfast, lunch and dinner.
Resorting to fast by a prisoner is a prison offence as per the state Prison Rules and this matter will be dealt according to the jail manual, he said.
The action likely to be initiated against Jagan includes reduced number of visits by his kin and
YSR Congress honorary president Y S Vijayamma, who had yesterday called off her indefinite fast opposing proposed bifurcation of Andhra Pradesh after she was forcibly shifted to a hospital in Guntur, had announced that her son and jailed Kadapa MP Jaganmohan Reddy will go on an indefinite fast seeking "justice for Seemandhra people."
As a precautionary measure, security was beefed up around Chanchalguda central prison with deployment of additional personnel from city police and also para-military forces besides the routes leading to jail were barricaded with barbed wires, another senior police official said.
Jaganmohan Reddy has been lodged in Chanchalguda jail since May 27 last year after his arrest by CBI on corruption charges.
Meanwhile, YSR Congress Party said that Jagan has begun indefinite fast at the jail demanding the Centre "maintain the status quo in Andhra Pradesh if it cannot do justice to all regions" in the light of proposed division of the state.
"It is believed that Jagan Mohan Reddy went on indefinite fast since this morning and a section of media has been trying to unleash false propaganda sowing seeds of suspicion about the fast while in custody though there are no restrictions or guidelines set for the protests programme," a YSRCP release quoted party spokesperson Ambati Rambabu as saying.
Jagan has been lodged in the jail for about 15 months in connection with an alleged disproportionate assets case.
"It is the right of every citizen to undertake any agitation programme unlike what is being projected by a section of media. Gandhiji went on indefinite fast in jail on many occasions.
"The media that is supportive of Seemandhra agitation trying to spread falsehood about the possibility of going on fast in jail is unfortunate," Rambabu said.
He appealed to the party cadre to join him in protest against the Centre's "unilateral" decision on the creation of Telangana, which is "not in the interests of both the regions".