India deployed tens of thousands of police to patrol major cities and posted sharpshooters on rooftops Tuesday as the country marked 59 years of independence under a terror alert.

Intelligence reports had indicated that Islamic militant groups might be plotting major attacks around the celebrations, which came a month after the Bombay train bombings that killed 207 people.

The U.S. Embassy warned last week that groups linked to Al Qaeda could target hotels, airports or historic monuments in New Delhi, Bombay or other cities.

In New Delhi, security forces shut all roads leading to the Red Fort — a 17th century sandstone structure built by Mogul emperors from where Prime Minister Manmohan Singh unfurled the national flag and addressed the nation.

No-fly zones were declared over New Delhi during Singh's address, and sharpshooters were posted on the rooftops of government and other high-rise buildings. Police checked every vehicle entering the city.

Authorities deployed more than 60,000 police and paramilitary soldiers across the capital, a city of 14 million people, where terror attacks were feared the most, a Home Ministry official said on customary condition of anonymity.

In Indian-controlled Kashmir, Chief Minister Ghulam Nabi Azad, the state's top elected official, and other officials were hurriedly whisked from an Independence Day celebration at a stadium, but police offered no explanation for their sudden exit.

Police also detained about 150 former militants in Indian-held Kashmir in a bid to prevent violence, said a police officer in Srinagar, the state's summer capital. Mobile phone service was switched off across the Kashmir Valley as a precaution.

In his address, Singh said terrorists were trying to derail India's booming economy and spark religious strife. He also repeated India's complaints that Pakistan's failure to control terrorist groups based in its territory was undermining the peace process between the nuclear-armed rivals. India suspects Pakistan-based Islamic militants were responsible for the July 11 Bombay bombings.

"Unless Pakistan takes concrete steps to implement the pledge it has made to crack down against terrorist groupings operating from its territory, public support (in India) for the peace process will be undermined," Singh said.

India gained independence from Britain in 1947, when more than 1 million people were killed as overwhelmingly Muslim Pakistan was carved from largely Hindu India.

In January 2004, Pakistan and India agreed to start a peace process to end their decades-old rivalry and dispute over Kashmir, the divided Himalayan region claimed by both sides. Pakistan agreed to crack down on militants who allegedly cross into Indian-held Kashmir to stage attacks.

Security was also heightened in Bombay on Tuesday, with paramilitary police patrolling outside railway stations, hotels, temples and mosques. Private security guards deployed sniffer dogs and frisked people at shopping malls and cinema halls in the country's entertainment hub.

Elite commandos guarded nuclear facilities, including the Bhaba Atomic Research Center in Bombay and the Kalpakkam nuclear reactor in Tamil Nadu. Airports across the country also were on high alert, and security was tightened around the Taj Mahal.