ISLAMABAD -- A suicide bomber on a motorcycle killed at least 34 people along a busy commercial strip near Pakistan's military headquarters Monday as the nuclear-armed South Asian nation struggled to protect its cities amid an army offensive against a remote Taliban stronghold.

The offensive was prompted by a wave of terror attacks that began in early October. Citing the rising violence, the United Nations on Monday announced it was pulling its staff from northwestern Pakistan, where the militants are strongest, and would...