Security was beefed up in Delhi after intelligence input suggested that two key members of terror group Jaish-e-Muhammed (JeM) have entered the national capital with the intention to carry out "high-profile attacks" and create "hostage crisis".

"We have inputs regarding two Jaish-e-Mohammed key members who have sneaked into Delhi and are suspected to be planning high-profile attacks or hostage crisis," PTI quoted a senior police official as saying on Sunday.

The security agencies had already put Delhi on high alert following terror attacks at the Indian Air Force base in Pathankot, Punjab, on Saturday. 

However, Delhi Police Commissioner B S Bassi held a meeting with top officials on Sunday after receiving inputs suggesting possible terror threat in the national capital and sought increased security measures.

Security has been tightened at the airport, railway stations and vital installations across Delhi.

"We have also got a few additional companies of paramilitary forces to increase security following the alert," the official said.

Later, Bassi posted a tweet asking Delhiites to be vigilant of anything suspicious. "Citizens' vigil against suspicious persons/objects/ activities is vital to counter terrorism. Report anything amiss no. 100 or helpline 1090," he tweeted.

The threat of the terror attack is a major concern for India as it is preparing for its 67th Republic Day celebrations. French President Francois Hollande is also scheduled to come to India as he has been invited to be the chief guest at the Republic Day parade on 26 January, 2016.

It is feared that the armed government troops that have arrived in Delhi for the Republic Day parade might become the target of the terrorists.  

"There is a possibility of terror attacks on isolated police stations or contingents of the armed forces. It is imperative for the local police to be prepared round-the-clock. It is also necessary that mock drills are carried out to assess the response time, status of weapons and equipment, mobility and coordination with the Special Forces," a letter by the Deputy Police Commissioner (Special cell) said, according to India Today.

Even as Delhi is being extra vigilant against possible terror attack or hostage crisis, confrontation between security forces and militants -- suspected to be members of JeM -- is underway at Air Force base in Pathankot.

The Indian security forces shot dead four militants on Saturday. However, during combing operation on Sunday they learnt about the presence of two more militants who were holed up inside the base, ensuing fresh gun-battle.

The Indian security forces on Monday launched fresh attacks on the hiding militants and gun-battle is still underway.

So far seven security personnel, including one National Security Guard Lieutenant Colonel, have been killed in the terror attack in Pathankot.