In one incident, a crude bomb was thrown at a mosque situated in the heart of Faizabad city late last night, police said today.
No one was hurt in the incident but glass of doors and windows was broken due to impact of the blast, police said.
Faizabad DM Anil Dheengra and SSP Mohit Gupta said investigation is being conducted into the bomb blast.
"It seems to be a well-planned conspiracy to create communal riots here but we will never allow any such incident," Gupta told PTI.
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"We have filed the complaint about the attack," said Mansur Ilahi, senior Samajwadi Party leader.
In a separate incident during the last night, idols in a Shiv temple in Wazirganj area of Faizabad city were found broken, police said.
This incident created tension locally but tempers were cooled by police intervention.
In the last few days, about half a dozen incidents of breaking and stealing of the idols from various temples have been reported.
In two prominent cases of idol stealing, the police acted promptly and recovered the stolen idols. However, the cases of the breaking of idols are yet to be cracked.
Highly placed intelligence sources said the attacks on both mosques and temples during the prominent Hindu festival Navratras indicate a well-planned strategy to create communal tensions in Faizabad, which is adjacent to Ayodhya.
Earlier on August 18 this year, during 'Sawan Mela' festival, some unidentified miscreants had tried set Jama Masjid in Faizabad on fire.