KABUL, Afghanistan — One minute, it was a wedding — nearly a thousand guests packed under one roof, a thin partition segregating them by gender. Men shimmied to a live band, women spun to a D.J. Their invitation cards read: We celebrate “with a world of hope and desire.”

The next minute, a suicide bomber walked into the men’s section of the Kabul hall and turned it into carnage. Dozens were dead, on the dance floor and around their tables. The band perished on the stage. The women were left broken, wailing, and searching.

Even by the standards of Afghanistan, where dozens are killed every day in a long war that seems out of control, the attack Saturday night was a shock. And not just because one bomber could end at least 63 lives, wound nearly 200, and scar hundreds of others for life.

It also was because of the choice of target and the timing, just as American negotiators are finalizing a deal with Taliban insurgents to extricate United States forces from Afghanistan after 18 years.