VOLGOGRAD, Russia — Eerily empty buses lumbered through the streets, police weighed down with body armor warily watched pedestrians near a fast-food restaurant, and members of Cossack units stood guard at bus stops. Volgograd was an ominous and jittery city Tuesday, after two suicide bombings in two days killed 34 people.

“People are afraid it will happen again; they’re trying not to go outside if they don’t have to,” said 20-year-old Yulia Kuzmina, a student. “We get a feeling that a war has started.” That is a worry that extends far beyond Volgograd.