Ukrainian Foreign Minister Pavlo Klimkin | Daniel Mihailescu/AFP via Getty Images Ukraine calls for sanctions against Gerhard Schröder Former German chancellor is Kremlin’s ‘most important lobbyist,’ says Ukrainian Foreign Minister Pavlo Klimkin.

Ukrainian Foreign Minister Pavlo Klimkin has called for sanctions against former German Chancellor Gerhard Schröder over his pro-Russia lobbying.

"It is important that there are sanctions against those who promote [Russian President Vladimir] Putin's projects abroad," Klimkin told German tabloid BILD in a report published late Sunday in reaction to a Wall Street Journal editorial that described Schröder as "Putin's key oligarch" and suggested it was a mistake to let him escape sanctions.

"Gerhard Schröder is the most important lobbyist for Putin worldwide," according to Klimkin, who called on the European Union to explore how to take action against him.

Schröder, who was elected chairman of the board of supervisors of Russian state-owned oil giant Rosneft last year, has come under fire for his close ties to the Kremlin.

Before leaving office in 2005, Schröder authorized the controversial Nord Stream pipeline project and took up a chairmanship at the company — which is controlled by Russia's Gazprom — several weeks later.

The project was heavily criticized by the Ukrainian government, because it would allow Russia to export gas to Western Europe via the Baltic Sea without granting access to Ukraine as a transit country.

Schröder also advocated that Europe continue to trust Moscow following Russia's illegal annexation of Crimea in 2014, and warned the EU and the United States against implementing further sanctions.

A spokesman for German Chancellor Angela Merkel rejected the idea of imposing sanctions against the former chancellor.

“The federal government, also the chancellor, do not see a reason to consider these kinds of things,” government spokesman Steffen Seibert said on Monday, according to German media.

Still, Schröder’s work has sparked criticism even within his own center-left SPD party.

“I wouldn’t be unhappy to see certain people leave the SPD,” SPD Bundestag member Ulrike Nissen wrote on Twitter, using the hashtag #Schröder.

MEP Elmar Brok, a foreign policy expert and member of Merkel's Christian Democratic Union (CDU), told BILD it was "a scandal that a former chancellor now represents the interests of Putin."