New Delhi, Aug 13 (IANS): An army of police and paramilitary personnel spread across the Indian capital as authorities issued a high alert ahead of Independence Day celebrations Thursday, officials said.

The main focus is on the 17th century Red Fort monument, from whose ramparts Prime Minister Manmohan Singh will address the nation Aug 15, and the areas around it in Old Delhi.

The first sign of the stepped up security was visible at Delhi Metro's 140 stations where a much more thorough checking than usual led to serpentine queues of commuters.

The Central Industrial Security Force (CISF), which guards the metro stations, asked passengers to hold their mobile telephones and wallets in their hands during security check -- a drill not normally followed.

"We are fully prepared to tackle any unwanted activities in the city," Special Commissioner of Police Deepak Mishra told IANS. But he declined to reveal specific details.

All vehicles entering Delhi from the neighbouring states of Uttar Pradesh and Haryana will be randomly checked at the border, said Additional Commissioner of Police (Traffic) Anil Shukla.

Delhi usually turns into a fortress ahead of every Independence Day Aug 15 and Republic Day Jan 26.

This time there was an intelligence warning of a possible terror attack in Delhi, police sources said.

At least five to six Central Reserve Police Force (CRPF) personnel along with Delhi policemen have been deployed at major intersections. Barricades have come up across the city.

"We have deployed around 10 CRPF companies," a CRPF officer told IANS.

Major shopping areas including at Karol Bagh, Connaught Place, Sarojini Nagar, Chandni Chowk and Khan Market as well as cinema complexes have been almost sealed off to regular shoppers and crowds.

More than 200 CCTV cameras have been installed around the Red Fort.

Entry of visitors other than passengers have been banned at airports till Aug 30, the CISF said.

Besides security personnel and commandos, officials in plain clothes as well as snipers will be deployed as usual in the Red Fort area.

The fort complex will see around 6,000 security personnel.

As in the past, police are scanning high-rise buildings, hotels, guest houses and markets in the area.

"Intensive checking has been started at the airport, railway stations, Metro stations, bus stops, markets and malls," said a police officer.

Delhi Police Commissioner Bhim Sain Bassi met police officers from neighbouring states Aug 7 to discuss security issues ahead of Independence Day.

"The objective was to share intelligence and inputs about various extremist outfits," Delhi Police spokesperson Rajan Bhagat told IANS.