India put airports in New Delhi, Bangalore and Chennai on high alert after a terrorist threat as US Secretary of State Condoleezza Rice said Pakistan has evidence to act against the suspects in last week's attacks in Mumbai and Pakistani President Asif Ali Zardari promised the visiting US secretary of state that his country would take “strong action” against any elements in his country involved in the siege. Security agencies in India stepped up their vigil after several threats, including one purported to have been sent by Deccan Mujahideen, which took responsibility for the attacks last week in Mumbai that killed 195 people. “A red alert has been sounded,” Digvijay Singh, commandant, Central Industrial Security Force, in charge of security at the Bengaluru International Airport, said in a telephone interview. “This is due to some intelligence inputs suggesting there will be attacks on the airport. One such is an e-mail from Deccan Mujahideen.” “This is a warning which we have received. We are prepared as usual,” India's air force chief, Fali Homi Major, told reporters Thursday. Security agencies in India have increased anti-sabotage units at the airport in Bangalore and extra policemen have been deployed, said Singh of the Central Industrial Security Force. Barricades have been set up on the route to the airport and passengers' bags are being checked. Heavily armed guards from India's Rapid Deployment Force manned roadblocks outside airports, while others patrolled inside airport buildings among passengers. Several extra layers of security were set up and some passengers had bags scanned with devices to check for explosives before entering terminals. “Passengers have been asked to pass through six-stage security checks,” said Brij Lal, a senior police official organizing security at the airport in the northern city of Lucknow. “A few commandos armed with AK-47 rifles are also being posted at the airport,” Singh said. Armed plainclothes officers have taken positions, he said. All three airports have been told to step up security, an official of the Bureau of Civil Aviation, a government body that handles civil aviation security, said in a telephone interview from New Delhi. The measures include increased frisking of passengers and searching of cars. “The government has to show to the people that they are taking high alert measures,” N. Manoharan, analyst at the Center for Land Warfare Studies, said in a telephone interview from New Delhi. While these may be tactics by the terrorists to confuse the security services, the “threat is imminent and they are going to strike somewhere,” he said. Zardari Thursday assured visiting US secretary of state that Pakistan will assist in investigation into last week's Mumbai attacks, according to a statement from the Pakistani president office. “The government will also take strong action against any Pakistani elements found involved in the attack,” Zardari told Rice, it said. “Pakistan is determined to ensure that its territory is not used for any act of terrorism,” the statement quoted Zardari as saying.