High alert has been sounded along the India-Pakistan border a day after the suicide bomb attack at the Wagah checkpoint near Lahore, even as the death toll climbed to 61.
Border Security Force (BSF) chief DK Pathak said Monday the BSF had received some inputs a fortnight ago that terror groups may try to carry out a possible strike during the beating retreat ceremony, hosted by border guarding forces of both nations.
A home ministry official too said there were alarms about a possible strike.
"India's external intelligence agency, Research and Analysis Wing, had got intelligence inputs some 15 days back indicating that the flag-lowering might be targeted by the Tehreek-e-Taliban Pakistan," he said on condition of anonymity.
Every day before sunset, soldiers from Pakistan and India gather at Wagah, the only road border crossing between Amritsar and Lahore, to simultaneously lower the two nations' flags.
Twenty people have been arrested over Sunday's bombing which took place 500 metres from the border on the Pakistani side at 6.12pm. Ten women, eight children and three security personnel were among the 61 dead.
Watch: India beefs up security post blast
No Indian troops were hurt but the blast left windows and doors of the BSF post shaking. Most of the people who died in the blast were returning from the ceremony.
"A large number of people were returning after watching Rangers flag ceremony at Wagah border when a suicide bomber blew himself up near one of the exit gates," Mushtaq Sukhera, inspector general (IG) of police of Punjab, said. He added three Pakistani Rangers were among the dead.
Pathak said there would be no beating retreat ceremony at Wagah border for three days from Monday at the request of Pakistan.
The BSF chief added his officers in Punjab had already undertaken "coordination" meetings with all intelligence, security and state government authorities in the light of the inputs they had received.
Land border trade between India and Pakistan came to a halt on Monday.
Customs officials in Attari, Punjab, said there was no trade activity from either side. They said that the trading activity was likely to remain suspended for another two days.
Hundreds of trucks from both countries carry products, including fruits and vegetables, through the land border trade.
Meanwhile, a militant group close to Pakistani Taliban, claimed responsibility for the deadliest attack to hit Pakistan in a year, saying it was a response to the Pakistani army's actions against their positions in tribal areas.
An 18-year-old bomber tried to enter the security perimeter of the border area complex but was checked by the Rangers and that is when he detonated the explosives strapped on his body, Punjab poilce IG Sukhera said. He was carrying 20 to 25 kg of explosives.
"I was sitting in my office near the border when I heard the blast. I rushed to the scene and saw scattered bodies, injured men, women and children and smashed cars," a Pakistani intelligence source said.
Security officials expressed fear that the teenager might have been trying to detonate himself further inside the complex that could have caused damage on the Indian side as well.
The dead and wounded were taken to Lahore's Ghurki hospital, where distressed relatives, weeping and hugging each other in grief, searched for their loved ones.
Live TV footage showed people drenched in blood and crying in pain as they were evacuated to hospitals, where relatives of the dead cried and beat their chests and heads. "My brothers, my two brothers… They both are dead," a man wailed.
"We received 35 bodies including those of women and children and 60 to 70 were wounded," deputy medical superintendent of Ghurki Hospital near the Wagah border crossing, identified only as Dr Khurram, told Pakistani television channels.
Lahore police chief Amin Wains confirmed it was a suicide attack. "Ball bearings were found at the scene," he said. TV channels showed images of gutted shops and buildings near the checkpoint.
Pakistan has been wracked by a homegrown Taliban insurgency that has killed thousands of people in recent years, but attacks have tailed off since the army launched a major anti-militant offensive in the northwest in June.
An HT team that visited the joint check-post in the night saw ambulances and other vehicles moving on the Pakistani side.
Indian Prime Minister Narendra Modi condemned the blast. "Terror attack in Pakistan near Wagah Border is shocking. I strongly condemn such a dastardly act of terrorism," Modi tweeted.
(With inputs from agencies)