Ukrainian President Volodymyr Zelensky warned German Chancellor Angela Merkel Sunday that the soon-to-be completed Nord Stream 2 pipeline carrying Russian gas to Europe was "a dangerous geopolitical weapon".

The comments came as the two leaders met in Kiev for a last time ahead of Merkel leaving office after 16 years in power next month and days after she held final talks with Russian President Vladimir Putin in Moscow.

Bypassing Ukraine and depriving the Western ally of essential gas transit fees Kiev estimates to be at least $1.5 billion per year, Nord Stream 2 is set to double Russian natural gas shipments to Germany, Europe's largest economy.

Kiev fiercely opposes the pipeline, arguing that it will increase Europe's energy dependence on Russia and Moscow's geopolitical clout.

"We view this project exclusively through the prism of security and consider it a dangerous geopolitical weapon of the Kremlin," Zelensky said during a joint press conference with Merkel.

While the main risks after the completion of the $12-billion pipeline beneath the Baltic Sea would be "borne by Ukraine", he said, it would also be dangerous "for all of Europe".

Merkel said Berlin agreed with Washington that "gas must not be used as a geopolitical weapon.

German Chancellor Angela Merkel will visit Ukraine ahead of her departure from office next month
German Chancellor Angela Merkel will visit Ukraine ahead of her departure from office next month POOL / Alexander Zemlianichenko

"It will come down to if there is an extension to the transit contract via Ukraine -- the sooner the better," she said, referring to the expiry of Moscow's agreement with Kiev in 2024.

While the construction of the pipeline led to tensions between Germany and the United States, Washington eventually waived sanctions against the Russian-controlled builder of the pipeline.

Merkel on Sunday sought to reassure Zelensky, saying that the Germany-US agreement specified "sanctions" if gas was "used as a weapon".

These commitments are "binding on future German governments", she noted.

She also said she had discussed with Putin extending Russia's transit contract with Ukraine past 2024.

The 10-billion-euro ($12-billion) Nord Stream 2 pipeline is set to double Russian gas supplies to Germany
The 10-billion-euro ($12-billion) Nord Stream 2 pipeline is set to double Russian gas supplies to Germany AFP / Odd ANDERSEN

"We feel a special responsibility" and "understand the big concerns that President Zelensky expressed," she said. "We take them very seriously."

The Ukrainian leader, however, said that while he and Merkel had discussed the extension, he had heard only "very general things".

In addition to the pipeline issue, the two leaders also discussed Ukraine's protracted conflict with pro-Russia separatists in its east, which has claimed more than 13,000 lives.

Merkel has helped mediate in the conflict, which broke out after Moscow annexed Crimea in 2014.

The following year she played a crucial role in clinching the Minsk peace accords, which helped halt the fiercest clashes.

But many in Ukraine think the deal, which assumes some autonomy for the breakaway parts of the Donetsk and Lugansk regions, was unfavourable for Kiev and is difficult to fulfil.

They also worry whether it will hold after Merkel's departure from office.

On Sunday, the German leader said she remained in favour of the current format of mediation between Kiev and Moscow led by Berlin and Paris because they have allowed the sides to "talk".

"Without that we'd have no contact whatsoever," she said

But she acknowledged that the results were "not satisfactory" because "Russia is directly involved in this conflict", which vindicated Ukraine's decision not to talk directly with the separatists.

"Therefore, we're in a situation where the talks are going in circles," she said.

Despite her strong backing of Ukraine, Merkel has also frustrated Kiev in her opposition to sending arms there.

On Sunday, Zelensky said that despite Germany's continued refusal to send weapons, Kiev was still "counting on it and expecting it".