Could Russia turn off the gas taps?
Russian President Vladimir Putin has warned European leaders that Ukraine's delays in paying for Russian gas have created a "critical situation".
Pipelines transiting Ukraine deliver Russian gas to several EU countries and there are fears that the current tensions could trigger gas shortages.
Mr Putin warned that Moscow could "completely or partially cease deliveries" if Ukraine does not settle its energy bill.
Daniel Sandford reports.
- From the section Europe