The Airbus 330 aircraft is being checked for explosives, by CISF and Bomb Disposal Squads.
"No explosive was found inside the cabin. The cargo portion is being checked," Minister of State for Civil Aviation Mahesh Sharma said, adding the process may take about three hours.
CISF Director General Surender Singh has briefed Home Minister Rajnath Singh on the situation.
Flight TKO65 sought an emergency landing after its pilot was informed about a message scribbled on the mirror of a washroom with a lipstick warning about the presence of a bomb in the cargo hold.
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Following this, the aircraft was diverted to Delhi where it landed at Indira Gandhi International Airport safely 1341 hours.
The entire area was cordoned off and fire brigade alerted before the plane was taken to the isolation bay for passengers to disembark and checks carried, sources said, adding the message appeared to be "hoax".
Commandos of the elite National Security Guard with their dog squads have been kept on stand-by.
Turkish Airlines said in a statement that its flight was diverted following a possible bomb threat.
"Turkish Airlines Bangkok - Istanbul flight (TK065, A 330
Aircraft, carrying 134 passengers) has diverted to Delhi after a possible bomb threat. The plane has already landed in Delhi and all of our passengers and cabin crew have been safely evacuated and taken to the terminal building," the airline said in a statement.