The Chhatrapati Shivaji International Airport in Mumbai, India, has been put on high alert after discovery of a threat message on a wall of a washroom on the airport premises.
The message that was found written on the wall of a terminal washroom on Saturday read: 'ATTACK BY ISIS DATE 10/01/15'.
This scrawled message was found a day after Air India's call centre in Thane received an anonymous phone call on Monday evening, warning of a 'terror attack', reported the Times of India.
The Central Industrial Security Force (CISF) has tightened security inside the airport and elaborate checks are being conducted outside the premises by Mumbai Police personnel.
CISF is currently going through CCTV footage to identify suspects who used the toilet late in the evening. The agency, which is responsible for the airport's security, is also questioning the housekeeping staff.
Deputy police commissioner (detection) Dhananjay Kulkarni was quoted by the Press Trust of India as saying: "We have been informed about the threatening message.
"We are looking into the matter. We are taking it very seriously and checking if it was just a mischief."
Different agencies are carrying out a probe. However, no case has been registered in the matter so far.
The Hindustan Times reported that the security alerts started on 23 December 2014, after the interception of a conversation between alleged terrorists.
"It seemed from their conversations that the 'terrorists' were to conduct a reconnaissance, but we could not take any chances and an alert was issued across the city," said a police officer, requesting anonymity.