Airports in India went on high alert Thursday following fresh attack warnings as officials said India suspects two senior leaders of a banned Pakistani militant group orchestrated the deadly Mumbai attacks. The alert comes as Pakistani President Asif Ali Zardari promised the visiting US secretary of state his country would take "strong action" against any elements in his country involved in the siege. The new alert that warned of possible airborne attacks focused on three major airports - New Delhi, Bangalore and Chennai - but security was stepped up across the country. No details about the threat were released. "This is a warning which we have received. We are prepared as usual," India's air force chief, Fali Homi Major, told reporters Thursday.