Russia and Ukraine wrangled over gas supplies again yesterday and two European Union states, cut off by the row for a freezing week, launched missions to plead for Russian gas flow to be restored.

European Commission chief Jose Manuel Barroso called the crisis "unacceptable and incredible" and warned the EU executive would advise the bloc's firms to sue Russian and Ukrainian energy companies unless gas supplies were restored quickly.

Russia began pumping gas meant for Europe via Ukraine on Tuesday, but the EU said little or none was flowing yet to countries downstream suffering urgent energy shortages.