German Chancellor Angela Merkel has said further sanctions may be imposed on Russia if it uses a controversial gas pipeline against Ukraine.
Mrs Merkel, on her final visit to Kyiv before leaving office, told Ukraine's President Volodymyr Zelensky she understood his concerns over the Nord Stream 2 project.
Mr Zelensky opposes the pipeline, which he says threatens Ukraine's security.
It will run under the Baltic Sea and double Russian gas exports to Germany.
Ukraine fears that the Russian-led Nord Stream 2 gas pipeline will tighten Moscow's grip over the region's energy supply and strengthen its influence.
During a joint press conference on Sunday, Mr Zelensky described the project as a "geopolitical weapon of the Kremlin", which he said would be "dangerous for all of Europe".
But Mrs Merkel, who is standing down as Germany's chancellor this autumn after 16 years in office, said Berlin agreed with Washington that Nord Stream 2 should not be used against Ukraine.
She said sanctions could be used against Moscow under an agreement between Germany and the US, if gas was "used as a weapon".
Mr Zelensky said he was concerned about what would happen in three years when the contract to deliver Russian gas through Ukrainian pipelines runs out. The loss of billions of dollars in transit fees would hit Ukraine's economy hard.
Mrs Merkel, who held talks with Russian President Vladimir Putin on Friday, promised to provide more than a billion dollars to help expand Ukraine's renewable energy sector.
Russia already supplies about 40% of the EU's gas - just ahead of Norway, which is not in the EU but takes part in its single market. The new pipeline will increase the amount of gas going under the Baltic to 55 billion cubic metres per year.
Mrs Merkel has tried to assure Central and Eastern European states that the pipeline would not make Germany reliant on Russia for energy.