Besides, intel inputs from US agencies have also alerted New Delhi of a possible ISI-sponsored terrorist attack in wake of abrogation of Jammu & Kashmir's special status guaranteed by Article 370.

Top sources in the Ministry of Home Affairs revealed that security arrangements have been tightened at all major airports, ports, vital installations, important government offices in Delhi, Mumbai and Bangalore.

Important premises including airports and railway stations in Punjab and Jammu and Kashmir were already put on alert after arms dropping by Pakistan through drones in Punjab in September. The National Investigation Agency (NIA) is coordinating with Punjab Police to unravel the conspiracy hatched by the ISI, using a splinter Khalistan terror outfit to execute the drone droppings.

The apparent terror threat seems to be a serious concern for the Prime Minister's Office (PMO). On Thursday, the Union Home Secretary, Director, Intelligence Bureau (IB) and and senior officials of the PMO had a brainstorming session, reviewing the steps taken by the states and central agencies to deal with the situation.

Sources in the MHA said that Home Minister Amit Shah has also been apprised of the measures taken at level of concerned states including Delhi Police. An IB alert earlier on Wednesday said that a highly trained module of terrorists of Jaish-e-Mohammed (JeM) has infiltrated into the national capital with an objective of launching sensational terror attacks during the ongoing festive seasons.

Subsequently, the Special Cell of the Delhi Police carried out raids at different locations and detained two suspects. The Delhi Police did not confirm about the detention or identities of the two suspects to IANS.

Meanwhile another report of IB says that more than 150 terrorists belonging to JeM and Lashkar-e-Taiba (LeT) have gathered near launching pads located inside Pakistani territory on the Line of Control bordering Poonch, Baramulla and Kupwara areas of Jammu and Kashmir.

ISI chief Lt General Faiz Hameed had last month toured PoK and held meetings with different outfits including JeM commanders. The report says on pressure of the ISI chief, JeM mastermind Masood Azhar was released from preventive custody despite being on the list of wanted global terrorists of the United Nations.

After Azhar's release, the Jaish cadres are in a pro-active mode, some of them had already infiltrated into Indian territory.