Ink was thrown on Aam Aadmi Party (AAP) MLA Somnath Bharti here on Monday while he was going to inspect some government schools.
Bharti was involved in a heated argument with police officials over his visit when an alleged right-wing activist threw ink on him.
The AAP leader had reached Rae Bareli on Sunday night, and was stopped from moving out of the guest house by the police on Monday.
After the incident, Bharti was detained in the guest house itself. The youth who threw ink on Bharti managed to escape.
Later, he was taken away to Amethi by the Amethi police.
An FIR has been registered against Bharti in Amethi for his alleged derogatory statement about the condition of hospitals in Uttar Pradesh.
The police spokesman, however, did not say whether Bharti had been arrested.
AAP MP Sanjay Singh, meanwhile, said that dictatorship in Uttar Pradesh was reaching a crescendo and efforts are being made to browbeat AAP leaders who raise questions on the poor conditions of health and education facilities in the state.