Taking no chances, the Union home ministry, based on unconfirmed inputs, has issued a terror alert for Mumbai, Delhi and four other undisclosed locations.

The Maharashtra police confirmed having received the alert from the central government. "We have beefed up the security apparatus in the state and Mumbai city," said a senior police officer from Mumbai.

The alert was sounded by the ministry after the Multi-Agency Centre (MAC) decided not to brush off a phone call to the National Investigation Agency (NIA) from Nigeria that six Nigerians trained by the Islamic State (IS) are trying to sneak into India from Pakistan.

The call from Nigeria on Tuesday this week sounded like a hoax, as like the infamous Nigerian fraud, it sought money transaction for further pinpointed information. Yet, the security establishment decided not to take it lightly.

The agencies are keeping their fingers crossed as it could be the first serious IS attempt to target India. The alert has been sent to Maharashtra, Gujarat, Punjab and Delhi police, sources said.

An earlier MAC alert had warned that a group consisting of six hard-core terrorists and led by a former Pakistani Army personnel, Mohammad Khurshid Alam, entered India on February 26 via Pathankot and it had hotels and hospitals as targets.

Sources, however, said that the alert was sounded not only on the basis of the call from Nigeria but has some other intelligence inputs to corroborate it.

Though an alert was issued for Holi, seeing the level of the threat, the Centre has increased its duration further.

Security agencies have been trailing Alam's footprints in Assam also. The MAC alert also spoke of terror threat in Assam as Khurshid Alam, in September last year, had visited Kharijia Darul Ulum Madarsa of Katajar, near Barpeta Road, Assam, and stayed there for five days.

Thereafter, he left for Chirang district that also lies in Assam but juts into the forested Bhutan border.

There are some other key elements to Alam's movements but the agencies requested not to publish those as it could foil their attempts to blow the lid off a terror module