Two loud explosions were overheard in the southern Ukrainian port city of Odesa on Sunday with black smoke seen rising from an industrial area.
"Odesa was attacked from the air. Some missiles were shot down by air defence," the city council said in a brief statement on the Telegram messaging app.
It said fires were reported in some areas but gave no indication what was hit in the attack.
The city, with Ukraine's largest port, has been preparing for weeks for a possible attack, given its strategic location on the Black Sea.
Meanwhile, Russian troops have been retreating in the northern parts of Ukraine from the capital Kyiv and Chernihiv in the north.
In towns and cities surrounding Kyiv, signs of fierce fighting were everywhere in the wake of the Russian redeployment.
Destroyed armoured vehicles from both armies lay in streets and fields along with scattered military gear.
Ukrainian officials and western allies have warned that Russian troops could escalate the conflict in the eastern Donbas region and focus on the besieged port city of Mariupol, located on the Sea of Azov.
Ukrainian presidential advisor Mykhailo Podolyak said on Saturday that Russia is prioritising moving east and south to control the occupied territories there.
Podolyak said he thinks Russia will try to create a strong foothold in the east with the support of air defence.
In the UK's Saturday defence intelligence update, the ministry of defence said that over the last week "there has been a concentration of Russian air activity towards south eastern Ukraine, likely a result of Russia focusing its military operations in this area."
Around 100,000 people are estimated to remain in the city that has dire shortages of food, water and medicine.
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