The US Embassy said terrorists were planning "imminent attacks" in India's capital and has warned Americans there to be vigilant.
Today's alert adding the word "imminent" appeared to be more urgent than an embassy advisory last month that cited increased indications of attacks in New Delhi.
The embassy noted that markets and other areas frequented by Westerners in New Delhi had been targeted in past attacks.
The alert said Americans in India should maintain "a high level of vigilance", remain aware of their surroundings and watch out for unattended packages.
Militants linked to Pakistan-based Islamic groups have been blamed for previous attacks in the Indian capital.Reuse content