Heavy security is in place in India ahead of the Muslim festival of Eid which falls this weekend.
The atmosphere has been soured by the recent attacks
Extra police have been deployed around mosques and shrines, after the bombings in the Indian capital Delhi last week in which 62 people died.
The attack affected celebrations for the Hindu festival of Diwali on Tuesday, with the city more subdued than usual.
No arrests have as yet been made over the bombings.
Reports say several raids were carried out in the town of Saharanpur in the northern state of Uttar Pradesh, the AFP news agency reports.
"Teams have been sent to several states, including Uttar Pradesh, and external links are also being looked into," a senior Delhi police official, Karnail Singh, told the Times of India newspaper.
No mood to celebrate
In the capital security is especially tight in the Muslim-dominated old city.
"The atmosphere has been marred by the bomb blasts," Mohammad Shahid, who sells prayer caps next to the country's biggest mosque - Jama Masjid - old Reuters.
"Many people are scared to come out shopping."
And in earthquake-hit Kashmir survivors said they were in no mood to celebrate.
"To celebrate Eid we require money to buy new clothes, meat and other items," the AFP news agency quotes Akbar Din, a labourer in Indian-administered Kashmir, as saying.
"I do not have a single paisa now," he added.
Aid workers warn that the impending winter could make matters worse for the survivors unless urgently needed aid reaches immediately.
In neighbouring Bangladesh, thousands of holidaymakers packed into buses and trains heading out from the capital Dhaka into the countryside.
Reports say an estimated six million of the city's 10 million people go home to their villages to celebrate Eid with their families.
But leave has been cancelled for police ahead of a regional summit, which is scheduled to take place in Dhaka next week.