New Delhi, Aug 14 (IANS): India braced itself to celebrate its 63nd Independence Day Saturday under the shadow of heightened security threats, fears of swine flu spreading and the country heading into its worst drought in the last two decades.

Prime Minister Manmohan Singh will unfurl the national flag from the ramparts of the Red Fort and address the nation for the sixth consecutive year and is expected to focus on these pressing concerns.

While the biggest celebrations will be in Delhi, other state capitals and district headquarters will host smaller flag-hoisting ceremonies.

On Saturday, a three-tier security ring will be thrown around the Mughal-built Red Fort.

The capital will be declared a no-fly zone for the morning and air defence guns will be placed at strategic locations to ward off possible aerial attacks by unmanned or microlight aircraft.

"India has become accustomed to heightened security provisions at this time of year but after the Mumbai terror attacks last November, the security establishment is taking no chances," said a senior home ministry official.

As the country's top leadership is expected to be in full attendance at the Red Fort, the historic monument will be turned into a citadel. For starters, the entire Red Fort complex has already been sanitised.

This year, the threats are from multiple sources. Indian intelligence reports indicate that Islamist groups based in Pakistan and Bangladesh are planning strikes on Indian soil. Indian Maoist groups are also reportedly plotting attacks.

In the southern city of Hyderabad, where the World Badminton Championships are underway, a thick security blanket has been thrown around the indoor stadium after a warning by intelligence agencies about a terror threat.

Security has also been beefed up across India, especially in New Delhi, Kolkata and Hyderabad after advisories were sent to the police to raise their levels of preparedness to face terrorist attacks in the run-up to Aug. 15.

The home ministry has warned that the Pakistan-based Lashkar-e-Toiba militant group was trying to sneak its operatives through the porous India-Pakistan border to stage attacks in New Delhi, Hyderabad and Kolkata around Independence Day.

Last week the Delhi Police detained two operatives of Kashmiri militant group Hizbul Mujahideen for allegedly planning terror strikes in the Indian capital.

Cadets from the National Cadet Corps will also participate in the flag hoisting ceremony at the Red Fort, while over 3,000 students from 32 government schools will sing the national anthem.

The Guard of Honour contingent for Manmohan Singh at the Red Fort will consist of one officer and 24 men each from the three defence services and the Delhi Police.

This year, with the Indian Navy being the coordinating agency, the Guard of Honour will be commanded by Commander Gurkeerat Singh Sekhon.