Indian security on edge for Independence Day

The celebrations on August 15 -- which mark India's independence from British rule in 1947 -- have been frequently disturbed by insurgent groups who use the national day to mount attacks and underline their presence, forcing heightened vigil.

But the July 11 train bombings in the country's financial hub which killed 186 people, the foiling of a plot to bomb transatlantic airliners by British police last week, followed by a US embassy warning of a likely al-Qaeda attack in Mumbai or Delhi, have unnerved security agencies this year.

"Intelligence inputs ... have indicated renewed determination of terrorist outfits to undertake terrorist acts, target prominent political leaders and symbols of national importance," said Ajay Chaddha, a top Delhi Police officer.

Thousands of policemen and troops were positioned across cities and sites considered to be targets of militants fighting Indian rule in disputed Kashmir as well as insurgent groups in the troubled northeast, officials said.

Snipers, metal detectors, x-ray machines, sniffer dogs, radio frequency jammers and security cameras were also being deployed and troops armed with machine guns were patrolling the airport in New Delhi, officials and witnesses said.

The threat is considered to be the highest in the capital as the main celebrations on August 15 are centred in the city with the Indian prime minister hoisting the national flag at a historic fort and addressing the nation from its ramparts.