Every day before sunset, soldiers from India and Pakistan face stand on opposite sides of the Wagah border crossing and perform an elaborate flag ceremony. The event, which has occurred daily since 1959, attracts a wide audience and is popular with international tourists. At its conclusion, each side folds their country's flag and the soldiers shake hands.

Sunday's ceremony at Wagah transpired as usual. But soon after its conclusion, a suicide bomber detonated 11 pounds of explosives attached to his body at a nearby checkpoint, killing 52 people and injuring more than 100 others. Pakistani officials believe that had the bomber detonated closer to the border, the death toll would have been far higher.

Exact location where blast took place: Blast inside / near the venue would have been more deadly. #Wagah #Lahore pic.twitter.com/ZCmJvPaCIf — Pakistan Army (@Pakistan_Army) November 2, 2014

Two Pakistani Taliban groups have claimed responsibility for the attack: Jamaat ul-Ahrar, which recently splintered from the Pakistani Taliban, and Jundallah, a veteran terrorist group whose bombing of a church in Peshawar killed 127 last year. In remarks to Dawn, a Pakistani news service, Jamaat ul-Ahrar spokesman Ehsanullah Ehsan claimed that the bombing was in retaliation for Pakistan's anti-jihadist military operations near the country's border with Afghanistan.

"We will continue such attacks in the future," Ehsan said.

Neither group cited Wagah's proximity to India as a justification for the attack. But the violence heightened tensions along one of the world's most contentious international borders. India and Pakistan have fought three wars against each other since achieving independence in 1947, and continue to dispute the sovereignty of Kashmir. In recent years, the two countries have cooperated over non-security issues like disaster relief, trade, and energy. But the potential for armed conflict is never far from the surface. India reportedly keeps 500,000 troops stationed in Delhi-administered Kashmir.

According to India's Hindustan Times, all but three of Sunday's victims were civilians, and no injuries or deaths were reported on the Indian side of the border.