German Chancellor Angela Merkel said on Tuesday that Russia's cut-off of the Druzhba pipeline is unacceptable and called for diversity of the energy supply in Europe.

"It is unacceptable when there are no consultations over such actions. This destroys trust again and again," Merkel said at a join press conference with EU Commission President Jose Manuel Barroso.

On Monday, a spokesman for Belarus' pipeline operator Belneftekhim said that the Druzhba pipeline "is not pumping oil in the direction of Poland, Germany and Ukraine under orders from Belneftekhim."

Merkel said she would tell leaders of Russia and Belarus that an advance warning would be least the EU expected in such a situation.

Earlier on Tuesday, in an interview with the German public television ARD, Merkel said that Europe should diversify its energy supply, questioning her country's plan to close nuclear power plants after an important oil pipeline for Europe was cut off.

"We must think about the consequences of shutting down nuclear power plants," Merkel said.

The German government decided in 2000 to gradually phase out all 19 nuclear power plants in the country by 2020.

Merkel said that for Europe, it is "smart not to be one-sidedly dependent on one supplier."

"Therefore one will also think about liquid gas, for instance the building of a large terminal near Wilhelmshaven, one must conserve energy, one must use renewable energy," she told the television.

Merkel made the call for diversified sources of energy one day after German Economics Minister Michael Glos issued an official statement over the closure of the Druzhba pipeline.

"I view the closure of the important Druzhba Pipeline with concern. I expect supplies through the pipeline to be fully resumed as quickly as possible," he said.

Belarus and Russia have been at loggerheads over oil transit since the two countries resolved a trade dispute over natural gas.

Russia is a major supplier of oil and gas for Europe. Germany, the largest economy in Europe, imports around 100 million tons of crude oil a year and about 20 million tons are supplied via the Druzhba pipeline.

About 30 percent of Germany's natural gas is also provided by Russia.

"The incident shows once again that a balanced energy portfolio is vital for a high level of energy security, and that there must be no one-sided dependencies," said Glos, whose country holds the presidency of the European Union.

New energy policies will be at the top of the agenda at the EU summit in spring, the minister said.