BERLIN (Reuters) - Germany must answer urgent, growing political concerns about the planned Nord Stream 2 gas pipeline project given Russia’s seizure of three Ukrainian ships and their crew off the coast of Crimea, a senior German conservative said on Sunday.

Christian Democratic Union (CDU) candidate for the party chair Annegret Kramp-Karrenbauer is pictured during a Reuters interview in Berlin, Germany, November 30, 2018. REUTERS/Fabrizio Bensch

Annegret Kramp-Karrenbauer, a top candidate to replace Chancellor Angela Merkel as leader of the Christian Democrats, told public broadcaster ARD it would be “too radical” to withdraw political support for the project, but Berlin could reduce the amount of gas to flow through the pipeline.

Russia is resisting international calls to release three Ukrainian ships seized last weekend in the Kerch Strait near the Crimea region that Moscow illegally annexed from Ukraine in 2014. Moscow has accused the 24 sailors of illegally crossing the Russian border, which Ukraine denies.

After meeting with Russian President Vladimir Putin, Merkel on Saturday called on Russia to release the sailors and allow free shipping access to the Sea of Azov, but stopped short of endorsing any additional sanctions against Moscow.

Kramp-Karrenbauer is a close Merkel ally but has taken a firmer stance on Russia’s actions in recent days. On Friday, she told Reuters the European Union and the United States should consider banning from their ports Russian ships originating from the Sea of Azov in response to the incident.

She told ARD on Sunday that it was time to draw a firmer line against Russian actions, including its annexation of Crimea and its support for separatists in eastern Ukraine.

“We have to acknowledge that the hard point has not been reached, otherwise Putin would not have taken this path,” she said, although she noted that Russia had continued to provide Germany with gas supplies even during the Cold War.

Her suggestion of banning Russian ships from European ports triggered criticism from some Social Democrats, including former foreign minister Sigmar Gabriel, who urged calm and accused Ukraine of trying to drag Germany into a war with Russia.

Justice Minister Katarina Barley, appearing on the same ARD programme on Sunday, said the incident still needed to be investigated, and cautioned against too-hasty conclusions.

The $11-billion Nord Stream 2 project, led by Russia’s Gazprom, aims to double capacity of the existing Nord Stream 1 pipeline from next year, bypassing traditional routes through Ukraine.

Businessman Friedrich Merz, the other top contender for the CDU leadership role, on Friday said escalating tensions between Russia and Ukraine had renewed debate over the pipeline.

“The more the conflict escalates, the more it raises the question: Is it really the right thing that we build this pipeline?” he said.

The United States, Ukraine and eastern European states oppose the pipeline, arguing that it will harm Ukraine and reduce the transit fees it now earns for piping gas. Washington also argues that the pipeline will leave Germany dependent on Russia for decades to come.