The massive fire that engulfed a fuel depot outside the Ukrainian capital on Monday has been localized and efforts to fully extinguish it are underway, a top emergency official said here Wednesday.

"There is no longer any threat of the fire spreading in the direction of the military unit, the nearby oil depot 'KLO' or the military airport," Mykola Chechetkin, head of the State Emergency Service, told reporters during a briefing.

He said the fire had been put out on 11 oil reservoirs, while six other fuel tanks are still burning.

Although an estimated 14,000 tons of oil products have been burned during the fire, local ecologists said that the contamination parameters in the area close to the fire site are within normal limits.

"There is a certain rise in the level of contaminants, but it is considerably less than the maximum allowable concentration," Volodymyr Tsyba, head of the Kiev regional administration's ecological department, told reporters.

The fire started at one fuel tank of the oil depot near Vasylkiv town, 38 km south of Kiev, on late Monday.

On Tuesday morning, the blaze spread to 16 other oil reservoirs following a massive blast.

According to the latest data unveiled by the country's Interior Ministry, at least four people, including three fire fighters, were killed and 12 others were injured in the blaze, while one fire fighter is still listed as missing.

The country's National Security and Defense Council has warned that the fire was threatening to spread to the military unit with a warehouse of munitions, a military airport of the Ukrainian army and another oil depot nearby.

The Interior Ministry said that a technical fault and violation of safety regulations are possible causes of the fire, while the company that owns the fuel depot, BRSM-Nafta, said the blaze may have been caused by arson.

Ukrainian prosecutors have opened a criminal investigation into the incident.