Bulgaria is to halt work on its Russian-backed South Stream gas pipeline following criticism from the EU and US.
Prime Minister Plamen Oresharski announced that he had "ordered all work to be stopped".
"We will decide on further developments following consultations with Brussels," he said after meeting with US senators.
The Gazprom-financed pipeline would ship gas to western Europe via the Balkans, thus avoiding Ukraine.
The European Commission had sent Bulgarian authorities a letter at the start of the month, asking them to suspend work on the project.
The EC claimed Bulgaria may have broken EU public procurement laws by choosing local and Russian bidders.
Bulgaria has previously said it is being targeted by Brussels as a means of retaliating against Russia over the situation in Ukraine.
If built, the pipeline would deliver 63 billion cubic metres of natural gas a year, via Bulgaria, Serbia, Hungary and Slovenia before entering Italy.
Construction work on the pipeline began in Bulgaria in October 2013.