The Ukrainian capital, Kyiv, has been hit by at least four explosions – with a presidential adviser blaming kamikaze drones sent by Russia.
“It shows their desperation,” said Andriy Yermak, head of Ukrainian President Volodymyr Zelensky’s staff.
And in the port city of Mykolaiv, sunflower oil tanks were set on fire by similar drones, said the city’s mayor.
A week ago, the capital was hit by Russian missiles at rush hour, part of nationwide attacks which left 19 dead.
A Ukrainian air force official said all the drones – believed to be Iranian-made – had flown into the country from the south.
Oleksandr Senkevich said three drones had ignited the tanks at Mykolaiv, one of Ukraine’s largest ports, late on Sunday evening, hours before the attack in Kyiv.
Monday morning’s attacks in Kyiv were from drones – the low buzzing of these slow-moving weapons is becoming familiar across the country.
Mayor Vitalii Klitschko said residential buildings in the central Shevchenkivskiy area had been damaged.
The city reverberated to the rattle of gunfire as anti-aircraft batteries frantically tried to shoot them down. Video on social media appeared to show one interception.
The explosions on Monday began at about 06:30 local time (03:30 GMT). The most recent was at about 08:10 local time.
Two were close to the city centre, with sirens and car alarms heard across the area.
“The enemy can attack our cities, but it won’t be able to break us,” said President Zelensky, describing the attacks as “terrorising the civilian population”.
What is being targeted is hard to determine. The mayor’s office says residential and non-residential buildings have been hit. Railway officials say explosions were seen close to Kyiv’s main station.
One Reuters journalist reported seeing fragments of a drone used in the attack that bore the words, “For Belgorod”.
The Kremlin has accused Ukraine of launching missile attacks on the city of Belgorod. Ukraine has denied this.
Two gunmen – who had volunteered to fight in Ukraine – killed 11 people on Saturday at a Russian military training camp in the Belgorod region of Russia, which borders Ukraine.
Recent attacks have targeted Ukraine’s energy infrastructure. It will be surprising if that is not the case again.
Writing on the Telegram social media site, Mr Klitschko said there were four strikes in Kyiv, although residents heard five or six explosions. He also told people to stay in air raid shelters.
But despite the warnings, the streets are far from deserted. Between the first and second set of strikes, plenty of people seemed to be going about their Monday morning business.
Mr Yermak described the kamikaze attacks as Russia’s “death throes” and said Ukraine needed more air defence systems “as soon as possible”.