NEW DELHI, Dec 4 (Reuters) - Indian has declared a security alert at three major airports, including Delhi and the IT hub Bangalore, and added extra checks to vehicles and luggage after warnings from intelligence agencies, officials said on Thursday.

Local television showed armed police guarding entrances to Delhi's international airport. Police cordons had also been set up outside the airport in the southern industrial city of Chennai.

The heightened security comes days after the militant attacks in Mumbai that killed 171 people.

The anniversary of the 1992 demolition of a 16th century mosque by Hindu groups in the northern town of Ayodhya is also marked on Dec. 6, officials said, an event which sparked violence between Hindus and Muslims. Indian television said the alert was issued after an email from Deccan Mujahideen, the same group that claimed responsibility for the Mumbai attacks. Officials said they did not have information about this.

"More checking of passenger luggage of people coming to the airport, more thorough checking of vehicles coming to the airport," Moushumi Chakravarty, a spokesperson for the Ministry of Civil Aviation, said.

"There are more security measures to control the airspace also. There are security personnel manning the perimeter of the airports." (Reporting by Matthias Williams: Editing by Alistair Scrutton)

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