At least nine people have been injured in two explosions inside the Jama Masjid (Grand Mosque) in the Indian capital, Delhi, police say.
One person was seriously hurt in the blast
The mosque's chief cleric, Imam Bukhari, told the BBC the blasts inside the complex came in swift succession. He has appealed for calm.
It is not clear what caused the blasts which came soon after Friday prayers.
The 17th century mosque is one of the largest in India. A bomb disposal squad is at the site, police say.
Delhi police chief KK Paul told the BBC that one of those hurt was in a serious condition. The other eight received minor injuries.
Religious leaders, including Imam Bukhari, were swift to call for calm and stress the need for communal harmony.
Prime Minister Manmohan Singh also called for calm and condemned the blasts in Delhi and in Srinagar, in Indian-administered Kashmir, where at least five civilians were killed in grenade attacks and shooting.
The explosions came within minutes of each other at about 1700 local time (1130 GMT).
"The blasts took place near a water tank used by worshippers," a mosque official, Mr Amanullah, told the BBC.
He said that most worshippers were inside the mosque and not by the tank when the blasts took place.
Imam Bukhari said he thought worshippers had been deliberately targeted.
"We did not see the first explosion but the second one definitely originated from a plastic bag that was kept inside the prayer grounds," Imam Bukhari told the AFP news agency.
"The second blast went off as people were helping those injured and if this is not a terror attack then what is?"
"There is anger among our people but I am appealing to them to maintain calm."
The Jama Masjid is located in Delhi's old city which is mainly populated by Muslims and has a history of religious tension.
Last month, suspected militants targeted the Hindu holy city of Varanasi, where simultaneous explosions killed 15 people.
In October last year, more than 60 people were killed and hundreds injured when three bombs exploded in busy shopping districts in the Indian capital.