On Friday, President Volodymyr Zelenskiy made a surprise push for fast-track membership in NATO and ruled out discussions with President Vladimir Putin, responding to Moscow’s announcement that it had seized four Ukrainian territories.

After Putin organized a ceremony in Moscow to announce the four partially occupied districts as seized Russian soil, Zelenskiy signed the NATO application papers in an internet video that was clearly designed as a powerful reply to the Kremlin.

“We are taking our decisive step by signing Ukraine’s application for accelerated accession to NATO,” Zelenskiy said in the video on the Telegram app.

The video showed Zelenskiy in combat fatigues announcing the membership bid and signing a document flanked by his prime minister and the speaker of parliament.

The announcement was likely to touch a nerve in Moscow which casts the NATO bloc at home as a hostile military alliance bent on encroaching on Moscow’s sphere of influence.

Before Russia sent its armed forces into Ukraine in February, Moscow was demanding legally binding guarantees that Ukraine would never be admitted to the U.S.-led transatlantic defense alliance.