BRUSSELS, Sept 3 (Reuters) - The EU executive said on Thursday the bloc could only slap new sanctions after a probe reveals who was responsible for what Germany says was a deliberate poisoning with a toxic nerve agent of Russian opposition leader Alexei Navalny.

European Union leaders did not mince words in expressing their condemnation of the suspected poisoning of Navalny, with calls growing to punish Russia for the use of the Soviet-style nerve agent, the same substance that Britain said had been used against a Russian double agent in an attack in England in 2018.

The bloc's chief executive, Ursula von der Leyen called it a "despicable and cowardly act" and German Chancellor Angela Merkel said it was "disturbing".

A European Commission spokesman, Peter Stano, on Thursday said there was no investigation into Navalny's case ongoing for now, that Russia needed to carry out an independent probe to bring perpetrators to justice and that the bloc would react based on Moscow's next steps.

German Chancellor Angela Merkel faced pressure to reconsider the Nord Stream 2 pipeline over the case of Navalny, while the Kremlin rejected accusations that Russia had been responsible and said it saw no grounds for sanctions against Moscow. (Reporting by Gabriela Baczynska, John Chalmers, Marine Strauss)