KYIV, Ukraine (AFP) — United States (US) President Donald Trump threatened Sunday to impose more sanctions on Russia, after the Kremlin unleashed its biggest-ever aerial barrage at Ukraine.

Russian missiles and drones rained down across Ukraine early Sunday, killing four people and setting government offices in the capital Kyiv ablaze.

Trump told reporters after the assault he was “not happy with the whole situation” and said he was prepared to move forward on new sanctions on Moscow.

Ukrainian President Volodymyr Zelensky said he was counting on a “strong” US response.

Russia has intensified its onslaught against Ukraine since a meeting between Trump and President Vladimir Putin on 15 August failed to make any breakthrough on a ceasefire.

After Sunday’s attack on Kyiv, flames could be seen rising from the roof of the sprawling government complex that houses Ukraine’s cabinet of ministers in the heart of the city — the first time it has been hit during the three-and-a-half-year conflict.

Drone strikes also damaged several high-rise buildings in the Ukrainian capital, according to emergency services.

Russia denies targeting civilians in Ukraine.

It said it struck a plant and a logistics hub in Kyiv, with the Russian defense ministry saying “no strikes were carried out on other targets within the boundaries of Kyiv.”

“It is important that there is a broad response from partners to this attack today,” said Zelensky in his evening address, adding that Putin was “testing the world.”

“We are counting on a strong response from America. That is what is needed.”

Last warning to Hamas

Trump said Sunday he was issuing a “last warning” to Hamas, saying the Palestinian militant group must accept a deal to release hostages in Gaza.

“The Israelis have accepted my terms. It is time for Hamas to accept as well. I have warned Hamas about the consequences of not accepting. This is my last warning,” Trump said on social media, without elaborating further.

In a statement released shortly after, Hamas said it was ready to “immediately sit at the negotiating table” following what it described as “some ideas from the American side aimed at reaching a ceasefire agreement.”

US news outlet Axios reported that White House envoy Steve Witkoff sent a new proposal for a Gaza hostage and ceasefire deal to Hamas last week.

The White House has not released any details about the proposal but late Sunday Trump said “you’ll be hearing about it pretty soon,” as he portrayed the negotiations in a positive light.

“We had some very good discussions. Good things could happen,” he told reporters. “I think we’re going to have a deal on Gaza very soon.”