All supplies of Russian gas via Ukraine to Bulgaria, Turkey, Greece and Macedonia were halted on Tuesday, officials in Sofia said, prompting emergency measures and the closure of two Bulgarian fertiliser producers.

Turkish Energy Minister Hilmi Guler confirmed that supplies to his country from a western pipeline passing through Ukraine had been completely cut as a result of the Moscow-Kiev gas row.

Also affected was Romania, where Russian gas supplies were reduced by 75 percent from contracted levels, the state-controlled Transgaz pipeline operator said.

"We are facing a serious gas crisis, in which Bulgaria is a victim of the conflict between Russia and Ukraine," Bulgaria's Prime Minister Sergei Stanishev said after an emergency meeting of government officials to discuss the situation.

He said no one had warned Bulgaria, which relies almost entirely on Russian gas for its needs, about the possible suspension in flows.

State gas monopoly Bulgargaz told industrial users it was suspending or cutting gas supplies to a minimum and urged them to switch to alternative fuels such as oil. Fertiliser producers Neochim and Agropolychim said they were forced to halt production.

Russia on Monday ordered a reduction in gas flows to Europe via Ukraine, a measure it said was to stop its neighbour from stealing fuel. Ukraine said the move would jeopardise supplies to Europe, which is facing freezing temperatures.

The gas row has raised new questions about Russia's reliability as an energy supplier and rekindled Western suspicions -- still fresh after Russia's war with Georgia last year -- that the Kremlin bullies its pro-Western neighbours.

"Russia and Ukraine must find an urgent solution because the energy systems of dozens of countries are at risk," Bulgarian Economy and Energy Minister Petar Dimitrov told national radio.

Sofia said the gas flow to Bulgaria and the transit to Turkey, Greece and Macedonia had been suspended as of 0130 GMT.

Turkey's Guler said his country had raised supplies of Russian gas delivered via a pipeline which passes under the Black Sea to 48 million cubic metres per day from 40 million.

EMERGENCY MEASURES

Bulgaria, where temperatures dropped below minus 15 degrees Celsius (5 Fahrenheit) overnight, will be worst hit because like Macedonia it has no access to alternative pipeline routes.

The government called on households to start using other means for central heating. It said heating utilities would start using oil and assured people they would not be left in the cold.

Stanishev said schools, kindergartens and hospitals would be a priority for Bulgargaz.

Gas accounts for less than 10 percent of Bulgaria's energy needs but is a crucial source in winter as heating utilities in the cities and bigger towns run on gas.

The country started pumping a maximum 4.3 million cubic metres of gas from its sole gas storage facility, which has total reserves of 570 million, officials said.

Neighbouring Romania decided to cut supplies to gas-fired power producers and switch to fuel oil and coal.

"We are enforcing measures to make sure none of the household consumers and industrial ones suffers from this situation between Russia and Ukraine," Prime Minister Emil Boc said after an emergency meeting with economy ministry officials.

Romania, which receives about a third of its gas from Russia, said it will use more gas from underground storage. It covers 65 percent of its needs with domestic production.

There was no immediate reaction from Greece, which can access additional supplies from Turkey.