Orange, white and green balloons were flying high above the heavily-guarded Red Fort in Delhi when the celebration ceremony of India's Independence Day ended peacefully on Tuesday morning.

Indian security departments would be a little relieved as the whole city has been highly alert of terrorist attacks since last week.

Previously, the U.S. embassy in New Delhi had warned the city, saying that al Qaeda may hit Delhi or Mumbai. And last month seven serial blasts rocked Indian economic hub Mumbai, killing 186 people.

On the way to the Red Fort where the ceremony was held and Prime Minister Manmohan Singh would make an address, four to five check points were set up, barricades built and armed police stopped every car to check and ask passengers' ID.

And within a radius of three km around the fort, all vehicles were blocked off except those with an invitation to the ceremony.

According to local media, about 4,000 security personnel, all heavily armed, are guarding the Red Fort. A no-fly zone has been declared and air defense guns have been placed to ward off possible aerial attacks by unmanned or light aircraft.

In a residential area named Vasant Vihar in south Delhi, the police guarded the entry of the market area and asked every car driver to open the trunk for check.

About 3500 security personnel were also deployed at various stations of Delhi subway.

Prime Minister Manmohan Singh said in his speech at the celebration ceremony that India is facing major threat of terrorism to its internal security.

"Terrorists want to undermine our growing economic growth, destroy our unity and provoke communal incidents. We cannot allow this to happen," he said.

The government will modernize, strengthen and properly equip the security forces and intelligence agencies, Singh said.

In Mumbai, which recently suffered terrorist attacks, security check became even tighter for the Independence Day.

Around 35,000 policemen are on duty in the city from Monday to Wednesday to ensure an incident-free Independence Day, an official said.

The Bhabha Atomic Research Centre in Mumbai has also been heavily guarded as intelligence agencies warned of a possible missile attack the nuclear establishment.

Even tourists to India's national landmark Taj Mahal are affected by the nervous atmosphere. They were banned of carrying water or other kind of liquids inside the monument.

Sand-bag bunkers have been put up beside the outer gates of Taj Mahal for a round-the-clock vigil by police personnel armed with automatic weapons.

India won independence and freedom from British colonial rule on Aug. 15, 1947. Every year official ceremonies are held in Indian capital and each state.

Source: Xinhua