Russian President Vladimir Putin heads for Belarus on Monday, fueling Ukrainian fears he intends to pressure his ally to join a new offensive, as Russian drones attacked Kyiv in the latest assault targeting key infrastructure, Ukrainian officials said.

Belarus allowed its territory to be used as a launchpad for Moscow’s invasion of neighboring Ukraine, but has not joined the fighting directly.

“Protecting our border, both with Russia and Belarus — is our constant priority,” Ukrainian President Volodymyr Zelenskyy said after a meeting on Sunday of Ukraine’s top military command. “We are preparing for all possible defense scenarios.”

Putin heads for Belarus for his first visit in 3-1/2 years with the Kremlin describing it as a broad “working visit” and talks with Belarusian President Alexander Lukashenko.

Lukashenko has said repeatedly he has no intention of sending his country’s troops into Ukraine. But Ukrainian officials have warned for months that Belarus could again serve as a base for a ground attack on Kyiv.

Russian troops that moved to Belarus in October will conduct battalion tactical exercises, the Russian Interfax news agency reported, citing the Russian defense ministry.

It was not immediately clear when and where in Belarus the latest in a flurry of recent exercises will start.

On Monday, Russian air raids hit “critical infrastructure” in and around Kyiv, Ukrainian authorities said. Air defense systems destroyed about 15 of 20 drones directed at the capital, they said. Private homes were also damaged in the wider Kyiv region, Governor Oleskiy Kuleba said.

Kyiv’s mayor said preliminary information suggested there were no deaths or injuries from the attack on the capital, and medics were working at the sites of the strikes in the Solomyanskyi and Shevchenkivskyi districts.

“As a result of the attack on the capital, critical infrastructure facilities were damaged,” Mayor Vitali Klitschko said on the Telegram messaging app.

Zelenskyy on Sunday again called for Western nations to beef up Ukraine’s air defenses after weeks of Russian air strikes targeted the energy network amid sub-freezing temperatures.

Several loud blasts were heard on Monday, but it was not immediately clear whether they were air defense systems destroying the drones or drones hitting their targets.

Emergency power cuts were re-introduced in Kyiv after the attacks, electricity provider YASNO said.

The 10-month-old conflict in Ukraine is the biggest in Europe since World War Two, killing tens of thousands of people, driving millions from their homes and reducing cities to ruins.

Zelenskyy told Ukrainians the armed forces were holding firm in the town of Bakhmut — scene of the fiercest fighting for many weeks as Russia attempts to advance in eastern Ukraine’s Donetsk region.

“The battlefield in Bakhmut is critical,” he said. “We control the town even though the occupiers are doing everything so that no undamaged wall will remain standing.”

Denis Pushilin, Russian-installed administrator of the portion of the Donetsk region controlled by Moscow, said that Ukrainian forces shelled a hospital in the Donetsk city, killing one person and injuring several others.

Reuters could not independently verify the battlefield accounts.

Putin casts what he calls Russia’s “special military operation” in Ukraine as a watershed moment when Moscow finally stood up to the Western bloc, led by the United States, seeking to capitalize on the 1991 fall of the Soviet Union by destroying Russia.