KIEV, Ukraine — Fire has engulfed a large section of the exclusion zone around the destroyed Chernobyl plant in Ukraine, Ukrainian authorities said today.

It was unclear if the blaze has hit parts of the zone heavily contaminated by radiation from the 1986 reactor explosion and fire, although authorities said the flames swept through about half a square mile.

Russian news agency Tass today quoted Ukrainian official Yuri Antipov, in charge of the exclusion zone, as saying the fire started Monday evening and was brought under control by late morning today.

A 20-mile zone around the plant is off-limits to most people except for workers constructing a new shelter to cover the destroyed reactor’s building, and to visitors on short trips. The explosion and fire left some sections of the zone heavily contaminated, while other parts were less damaged.

Radiation levels in the areas have not changed, Victoria Ruban, a Kiev representative of the Ukrainian State Service, was quoted as saying.

This is the second fire in the off-limits zone in three months. The forest fire in April swept through 400 hectares and was described as the first fire in the area in more than two decades.