CARACAS, Venezuela  A sweeping power failure left Venezuela’s largest cities without electricity on Tuesday, snarling traffic, halting subway trains underground and mobilizing police forces here in the capital to thwart possible public disturbances.

Government electricity officials gave different reasons for the blackout, which began at 4 p.m. here and lasted more than two hours in parts of Caracas. Initially they said it was set off by peak electricity usage on a hot day, but later said a forest fire in Guárico, a state in north-central Venezuela, had caused the shutdown.

The power failure affected at least 11 of Venezuela’s 23 states. Among the hardest hit was Zulia State, home of Venezuela’s main oil fields and Maracaibo, the second-largest city. Power remained out in most of Zulia well into Tuesday evening, according to radio reports, but it was unclear if oil output from wells around Lake Maracaibo was affected.

“Zulia was the most affected,” Gen. Hipólito Izquierdo, head of the country’s electricity authority, said on state television. “But we have recuperated more than 60 percent of what was affected in the blackout.”