Three militant groups have separately claimed responsibility for the suicide attack at the Wagah checkpoint near Lahore that killed at least 61 people including 10 women, eight children and three securitymen on Sunday evening.
Pakistan, however, held the beating retreat ceremony on Monday evening amid reports that the daily military ritual would not be organised at Wagah after Sunday's bombing, which took place on the Pakistani side some 500 meters from the international border at 6.12pm.
Border Security Force (BSF) chief DK Pathak had said on Sunday that Pakistan had requested India not to conduct the ceremony for three days. If this had happened, it would have been for the first time since the two countries went to war in 1971.
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.
Most of the people who died in the suicide bomber attack were returning from the ceremony.
Officials said the changed plan to allow the ceremony on Monday had been communicated to the BSF by the Pakistani Rangers, a PTI report filed from Lahore said.
The gallery on the Indian side was empty, while a large number of people gathered in the Pakistan gallery and raised slogans.
BSF officers said visitors on the Indian side were turned back earlier in the day after Pakistan's request that the ceremony be suspended for three days.
Meanwhile, Pakistani Prime Minister Nawaz Sharif vowed strong military operations against militants in the wake of the deadliest attack to hit the country in six months.
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.
Sharif and Indian Prime Minister Narendra Modi both condemned the latest strike.
Sharif ordered an inquiry into the attack and sought a report from Punjab chief minister, Shahbaz Sharif. Punjab law minister Mujtaba Shujaur Rehman claimed that the suicide bomber managed to cross four security checkposts on GT Road.
No Indian troops were hurt on Sunday, but the blast left windows and doors of the BSF post shaking on the Indian side.
IED found near parking area
An improvised explosive device (IED) was found from the parking area of the Wagah border on Monday. The Bomb Disposal Squad (BDS) was called to the site for inspection after the recovery. The BDS then launched search operations surrounding Wagah border, The Nation newspaper reported. Pakistani security forces also began search operation in nearby villages and areas and rounded up several suspects.
High alert sounded, trade halted
BSF chief Pathak said 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.
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 (TTP)," he said on condition of anonymity.
Land border trade between India and Pakistan came to a halt on Monday in the aftermath of the suicide bomb attack.
Customs officials in Attari, Punjab, said there was no trade activity from either side. They added 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.
Bereaved relatives at a hospital in Lahore where people injured in Sunday's blast are being treated.(AFP photo)
Al Qaeda-affiliated militant group Jundullah (Soldiers of Allah), a splinter group of the TTP, was the first to claim the responsibility for the attack.
Taliban splinter group Jamaat-ul-Ahrar too said its bomber, Hafiz Hanifullah, carried out the attack. Later, a lesser-known Mahar Mehsud group also claimed responsibility for the bombing.
Jamaat-ul-Ahrar said on its Twitter page the attack was a warning to both Pakistan and India and that such an assault could also happen across the border. It refuted claims of other groups owning the attack.
Jamaat-ul-Ahrar also criticised Jundullah as a "fake" Iranian group.
Jamaat-ul-Ahrar had recently separated from the TTP after the army launched an operation in North Waziristan in mid-June. Led by Omer Khalid Khurasani, it is believed to be capable of lethal attacks.
Jundullah was also part of the TTP until last year when Hakimullah Mehsud, now slain, led the militants.
It had been involved in several high-profile attacks, including the strike on Crops Commander of Karachi in 2004, murder of 10 climbers in Gilgit-Baltisitan in 2013 and Peshawar Church bombing of last year.
This group also claimed responsibility of last month's attack at Maulana Fazlur Rehman who survived the suicide bombing.
The conflicting claims show the ongoing war among various militant outfits trying to replace the TTP which has been weakened by military operations and defections.
Last month, six important Taliban commanders joined the West Asian group the Islamic State (IS), also known as the ISIS or the ISIL.
Death toll 61
The overnight death toll in the suicide attack mounted to 61 on Monday afternoon. Security agencies have arrested about 20 suspects from the Indo-Pak border area.
Ten women, eight children and three security personnel were among the 61 people who have died in the attack.
Over 100 people were injured in the incident and are being treated in different Lahore's hospitals where emergency has been declared.
"The death toll of the devastating suicide attack at Wagah border has risen to 61. The condition of some injured is still critical and the doctors are battling to save their lives," Punjab Emergency Services Rescue spokesperson Jam Sajjad told PTI.
About 43 bodies have been handed over to the families, while the remaining are yet to be recognised, Sajjad said.
Lahore police spokesperson Niyab Haider Naqvi said, "The law enforcement agencies have launched operation in the residential areas in Wagah and taken about 20 suspects into custody."
"A joint investigation team of police, Rangers and intelligence agencies have started its probe into the incident. The army and Rangers along with police will provide security to Ashura processions in Lahore and they have been put on high alert in the wake of Sunday's attack."
According to a preliminary investigation report submitted to the inspector general (IG) of Punjab police, Mushtaq Ahmed Sukhera, the suicide bomber, believed to be in his early 20s, had been staying in the Wagah border area since many days.
"It is also suspected that the handlers of the suicide-bomber were also present near the blast site to ensure the execution of their plan," the report says.
At least 15 to 20kg of explosives were used in the blast with some of the explosives in the attacker's suicide jacket and the remaining being carried by him.
Pak offers security to Sikh pilgrims
Pakistan will provide complete security to more than 2,000 Sikh pilgrims from India arriving in Lahore on Tuesday for the three-day birth anniversary celebrations of Guru Nanak, an official has said, in the wake of the Wagah border suicide attack.
"We will ensure this (Wagah border-like bombing) does not happen again, particularly when over 2,000 Sikh pilgrims arrive at Wagah Railway Station," Evacuee Trust Property Board (ETPB) chairman Siddiqul Farooq had said on Sunday.
Watch:India beefs up security