TEHRAN, Iran — Rescuers dug with their bare hands Monday through the debris of buildings brought down by a powerful earthquake that killed more than 400 people in the once-contested mountainous border region between Iraq and Iran, with nearly all of the victims in an area rebuilt since the end of the ruinous 1980s war.

Sunday night’s magnitude 7.3 earthquake struck about 19 miles outside the eastern Iraqi city of Halabja, according to the most recent measurements from the U.S. Geological Survey. It hit at 9:48 p.m. Iran time, just as people were going to bed.

The worst damage appeared to be in the Kurdish town of Sarpol-e-Zahab in the western Iranian province of Kermanshah, which sits in the Zagros Mountains that divide Iran and Iraq.

Residents fled into the streets as the quake struck, without time to grab their possessions, as apartment complexes collapsed into rubble. Outside walls of some complexes were sheared off by the quake, power and water lines were severed, and telephone service was disrupted.