Russia unleashed yet another massive aerial bombardment aimed at Ukrainian cities and towns before dawn on Monday, pressing its advantage as the United States increasingly removes itself from the conflict and diplomatic efforts to end it.

At least 355 Russian drones swarmed the skies across Ukraine and bombers unleashed nine missiles, Ukraine said. The attack followed criticism by President Trump of President Vladimir V. Putin of Russia, whom he accused on social media of going “absolutely CRAZY” in his bid to conquer Ukraine.

But Mr. Trump, speaking to reporters before boarding Air Force One on Sunday, gave no indication that he is willing to provide Ukraine with military assistance. He also declined to answer questions about whether the attacks will lead to a change in policy.

Over the past week, Russia has directed at least 1,390 drones and 94 missiles at targets across Ukraine, the Ukrainian Air Force said. The attacks have killed at least 30 civilians and injured more than 163, Ukraine says.

The campaign comes a week after Mr. Trump spoke to Mr. Putin by telephone and appeared ready to abandon his efforts to secure a cease-fire.

Russia has clearly seen an opening as the United States — long the main arsenal of Ukraine’s resistance — pulls back from the diplomatic process and resists supplying Kyiv with additional military assistance, according to analysts.

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