Later in the day workers from Bulgaria's Kremikovtzi steel mill rose in protest and the rally turned violent as they tried to storm the building of the Economy and Energy Ministry.

Two people were arrested.

The protesters demanded an explanation for the cut in gas supplies to the plant and its looming shut-down from Economy Minister Petar Dimitrov, whose department holds a 25% stake in Kremikovtzi and is in a position to exert pressure.

Trade union leaders added fuel to the protest, saying that the smelter's major production units are being closed at a time when there is a real chance for the implementation of a recovery plan.

This will rob the plant of the possibility to recover even if an investor declares interest in it, the trade unions said.

The distribution firm Bulgargaz had warned more than a month ago that it would cut off deliveries over unpaid bills, closing the smelter's major production units.

The sprawling communist-era behemoth currently owes Bulgargaz BGN 105 M and according to to the distributor director Dimitar Gogov the likelihood of this sum ever being paid is very slim.

The plant near Sofia was declared insolvent in August last year with debts exceeding EUR 1 B. It is a big source of pollution and urgently needs re-furbishing.

Kremikovtzi, one of Bulgaria's biggest companies, provides jobs for over 5 000 people and its future is a politically sensitive issue ahead of the general elections in the summer.