Russian President Vladimir Putin will hold a meeting of his national security council on Monday, Kremlin spokesperson Dmitry Peskov told Russian state-owned news agency TASS on Sunday, following a fiery explosion on a strategic Crimean bridge on Saturday.

Although Peskov declined to say whether they would discuss the explosion on the Kerch Bridge connecting Russian-occupied Crimea to Russia, the blast that partially destroyed Putin’s pet infrastructure project — which is key to supply Russia’s military fighting in Ukraine — is bound to be on the security council’s agenda.

Over the past weeks, the Kremlin has been making thinly veiled threats to use its nuclear arsenal against Ukraine as Kyiv regains territory Russia has occupied in its invasion of the country.

The latest Russian official to sabre-rattle was Col. Gen. Andrey Kartapolov, who heads the defense committee of the State Duma.

“There will be an answer” that “all [Ukrainians] will feel” from the Russian side if Ukraine is found to be responsible for the blast that blew damaged the Kerch Bridge, Kartapolov told Russian news outlet Vedomosti on Sunday. “What the answer will be, we will find out. Our President and Supreme Commander-in-Chief never does what ‘partners’ expect from him. He does what is not expected of him,” Kartapolov said.

The Ukrainian government so far hasn’t been commenting about the origins of the apparent bombing. The country’s security service posted a cryptic message on Telegram Saturday after the blast, which reads: “Dawn, The bridge is well ablaze; Nightingale in Crimea, The SBU [Ukrainian security service] meets,” with a picture of the damaged bridge.

Russia opened an investigation into the explosion, and Russia’s Foreign Ministry is pointing the finger at Ukraine. “The reaction of the Kyiv regime to the destruction of civilian infrastructure testifies to its terrorist nature,” ministry spokesperson Maria Zakharova said, according to Russian news outlet Kommersant.

Kremlin spokesperson Dmitry Peskov declined to say whether they would discuss the explosion on the Kerch Bridge connecting Russian-occupied Crimea to Russia

Fear is mounting that Russia might resort to a nuclear response. Pope Francis on Sunday said that “we should not forget the danger of nuclear war,” asking “Why don’t we learn from history?”

Meanwhile, Ukraine’s Defense Ministry said the Russian army killed some 17 civilians in the Ukrainian area of Zaporizhzhia on Sunday.

“A missile attack on the civilian population of Zaporizhzhia destroyed residential houses, where people slept at night, lived, didn’t attack anyone,” Ukrainian President Volodymyr Zelenskyy said.