KIEV, June 2 (Xinhua) -- At least five people were killed when a blast rocked a rebel-held local administration building in Ukraine's eastern city of Lugansk on Monday, local media reported.
"Five people were killed. Many people among the civilians were wounded," Konstantin Knyrin, the head of information center "The southeastern front," was quoted by Interfax-Ukraine news agency as saying.
According to leaders of the self-proclaimed Lugansk People's Republic, a "fighter jet attack" was possibly behind the explosion.
Witnesses said "Ukrainian fighter jets were seen flying over the building prior to the incident."
However, spokesman of the government's military operation in eastern regions, Alexei Dmitrashkovsky, ruled out a possibility of Ukrainian troops attack on insurgents.
"Careless and inept handling of small arms and explosives was the most likely cause of the explosion," Dmitrashkovsky told local radio "Svoboda."
Reports in social media said that a huge fire broke out following the blast and many wounded people might still be trapped in the building.
Firefighters and ambulance vehicles arrived at the site.
There had been no official word on the cause of the incident and the exact number of casualties.
Fierce clashes between Ukrainian government troops and armed activists are underway in Lugansk and its neighboring Donetsk regions since early April, after insurgents established "people's republics" in their regions, seeking independence from Kiev.
The Ukrainian military launched an "anti-terror" operation in the eastern regions on April 13.