"We are very concerned with the latest news from Ukraine and the comments of the [Russian] prime minister [Vladimir Putin]," Barroso told a news conference after receiving Bulgarian Prime Minister Sergei Stanishev.
Hours before, Russian Prime Minister Vladimir Putin warned that Moscow would halt gas deliveries to Ukraine if payment were not received by Saturday, and this could also affect supplies to Europe.
A January dispute between Russia and Ukraine led to Russian gas supplies to Europe being severed for almost two weeks, triggering the EU's worst-ever energy crisis.
"We have already [...] stressed our strong condemnation of this kind of situation," Barroso told reporters.
"I think the credibility of Russia and Ukraine will of course be affected if we have another gas crisis," he added, standing next to the leaders of one of the countries worst-hit by the January gas shut-off.
The European Union has monitors in place to check on the flow of Russian gas through the key Ukraine pipeline, and Barroso said their numbers could be boosted if necessary.
Stanishev, speaking alongside Barroso, said a situation where countries are held "hostage" on gas supplies is unacceptable. Bulgaria was the most affected country during the January gas crisis.
Barroso made it clear that the Commission would not accept the reopening of nuclear units at the Kozlodui nuclear power plant, which Bulgaria had closed as part of its accession deal. But he but said that the Commission will examine demands by Sofia for additional decommissioning funding. Barroso also said that the Commission could provide support to Bulgaria by granting of over 500 million Euros in the form of preliminary payments along European programmes.
Stanishev said these demands were legitimate, as Slovakia and Lithuania had been benefiting from more generous decommissioning assistance.
Political heat
Putin made his statements after Ukraine's SBU security service tried yesterday (5 March) to gain entry to the offices of the authority overseeing Ukraine's gas pipelines. It was the second such incident in as many days apparently connected to Ukraine's gas deals with Russia.
The raids also served to highlight worsening tension between Ukrainian President Viktor Yushchenko and Prime Minister Yulia Tymoshenko: former allies now at loggerheads.
Timoshenko, addressing her cabinet, said the security forces were out of control and acting at the president's behest. Yushchenko's spokesperson said the SBU's first raid on Naftogaz had acted within the law.
In the meantime, Gazprom received $310 million from Ukrainian state energy firm Naftogaz for February gas deliveries, but a further $50 million was still owed, the Russian gas export monopoly said in a statement.
(EurActiv with Reuters)
